Embedded Files
Past Conferences/Workshop in Astrophysics/Gravity at Presidency University
Advanced School on Gravitational Waves
12th to 16th December, 2016, Amal Kumar Raychaudhuri Lecture Theater
Sponsored by the TPSC program (SNBNCBS) and IUCAA
https://gwschoolpu.weebly.com/
Universe after the first 200 million years
11th-13th December, 2017, AJC Bose Auditorium
National conference and workshop sponsored by SKA India (DAE)
https://presi21cm.wixsite.com/conference
One day regional conference, August 9th 2014, AJC Bose Auditorium
Topical Conference on Gravity and Cosmology (TCGC)-Eastern Region (2nd installment)
Special Events
Special Events
13. Dr. Srilekha Raha Memorial Lecture
Speaker: Prof. Supriya Chakrabarti, UMass Lowell
Title: Forest Structure Measurements Using a Novel Two-Wavelength Lidar System
January 14th 2025, @ Dr. Srilekha Raha Memorial Smart Computer Room
Photos and Video Link
https://photos.app.goo.gl/67FQjHNednhrQYMQ7
https://www.youtube.com/watch?v=O2Lu664ZUgk
12. শতবর্ষে বোস পরিসংখ্যান তত্ব
শ্রী সত্যেন্দ্রনাথ বসুর প্রবর্তিত বোস পরিসংখ্যান তত্বের শতবর্ষ পালন ।
অনুষ্ঠানের বিবরণ: তারিখ: ২০শে নভেম্বর, ২০২৪; স্থান: এ. কে বসাক সভাগৃহ, প্রেসিডেন্সি বিশ্ববিদ্যালয়
Photos and video links
https://photos.app.goo.gl/R4Q9TJGcaU5Gswna9
https://youtu.be/wDmrhPWPeA0?si=3bvKwa47Plv4Nw0D
https://youtu.be/icZ1llKzdCs?si=4nt1x-zRjJ-0T3pE
Doordarshan Coverage
https://www.youtube.com/watch?v=r1o30pfEI3g
11. A Seminar series on 'The Idea of a University in the 21st Century' Presented by SOA
21.8.24 : Prof. Nirmalya Narayan Chakraborty, Honorable VC, PU
Title: University: An Intellectual Community
28.8.24 : Prof. Sugata Bose, Havard University
Title: In Defense of Academic Freedom
4.9.24 : Prof. Malabika Sarkar, TCG CREST
Title: Dissolving Boundaries: The Future of Universities in 21st Century India
11.9.24: Prof. Sabyasachi Bhattacharya, TIFR
Title: "Of Light, Of Liberty and of Freedom"
Some glimpses:
https://photos.app.goo.gl/qzuZ8wZqsM7FJyvy5
10. Conference on Blazars and Restless AGN (COBRA)-2024: A High Energy View
A national conference sponsored by IUCAA and the BRNS (July 22nd-26th 2024) at the PCM Auditorium
Convener: Dr. Ritaban Chatterjee
https://cobra2024.weebly.com/
Some glimpses:
https://photos.app.goo.gl/hy6jnNxXjaSouZxw8
9. Prof. Shyamal Sengupta Memorial Symposium on "Towards Realising SSG's Dream: Testing the Quantumness of Increasingly Massive Objects."
Date, Time & Venue: 24th April, 2024, 2.00PM at PCM Auditorium.
Speaker: Prof. Dipankar Home, J. C. Bose Institute, Kolkata.
The talk will be followed by a tribute session chaired by Prof. Biswarup Mukhopadhyaya (IISER Kolkata), where SSG's former students and acquaintances will reminisce about his work and life.
Some glimpses:
https://photos.app.goo.gl/HNdTrSGk1f4cX5SL8
8. Presision 2024 - The presidency physics Summit.
Date, Time & Venue: 20 and 21st Apr 2024, Day Long at PCM Auditorium.
Speaker: Miscellaneous
About the Event: The flagship event of Presision, the famed Undergraduate Symposium, will be organized this year as well as a part of Presision. It is a terrific opportunity for Bachelor's, Master's, and early-stage MSc-PhD students to present their original research work, done during their undergraduate studies, on any branch of physics, in front of a like-minded audience of eager young physicists from across the country. Don't miss this opportunity to join the forefront of the student-driven Physics Community!
some glimpses:
https://www.youtube.com/live/JXQRpZCZs5A?feature=shared
https://www.facebook.com/presiphysicsfest
7. International Astronomical Union-Office of Astronomy for Education Teacher Training Workshop (Dec-1st & 2nd 2023)
A first of its kind workshop involving a university (Presidency University), College (Saint Xaviers College), and a School (Modern High School International) to bridge the gap at different levels of teaching with particular focus on the state of astronomy and astronomy education in India.
Some glimpses:
https://youtu.be/60VyVddGu7s
https://youtu.be/iGvnB8PuiwM
https://photos.app.goo.gl/kbgd5pDLqLrFK1C8A
6. মাতৃভাষায় বিজ্ঞান:
বক্তাঃ অধ্যাপক বিমান নাথ, রামন গবেষণা কেন্দ্র, বেঙ্গালুরু
বিষয়ঃ গ্যালাক্সির অশনি সংকেত
সময় ও স্থানঃ ৩০ নভেম্বর, দুপুর ২টো ৩০ মি, এ. কে. বসাক প্রেক্ষাগৃহ
https://photos.app.goo.gl/TC1YvCLFnag1WjgC7
https://www.youtube.com/watch?v=27S2Jheock0
5. Special Lecture by Prof. Rangina Hamidi
Thunderbird School of Global Management, Arizona State University
Title: "Women and Development"
Nov 21st, 11AM, P C Mahalanobis Auditorium.
https://photos.app.goo.gl/jPEdfhsMemJx1vhT8
4. Teaching Learning Workshop
Invited Lecture: Prof. M. Sivakumar, Hyderabad Central University
Title: "Physics Higher Education, Problems and Prospects"
Panel Discussion: The Changing Face of Higher Education in India
Panelists: Prof. M. Sivakumar (HCU), Prof. Parthasarathi Majumdar (IACS), Prof. Suparna Roychowdhury (St. Xaviers College), Prof. Raka Dasgupta (CU), Prof. Partha Ghosh (Bangabasi College), Moderated by Prof. Suchetana Chatterjee
Date and Time: April 12th, 2.30PM at P. C. Mahalanobis Auditorium
https://photos.app.goo.gl/gz1UbnfsRCuJQMMD7
3. The 4th AKR Memorial Lecture (Centenary Tribute)
Speaker: Padmabhusan Prof. Ashoke Sen
8th April 2023, Meghnad Saha Lecture Theatre
https://youtube.com/live/3RnhKftWIMk?feature=share
https://photos.app.goo.gl/KJTUwMt6hWfAqG4N6
Doordarshan Coverage Link of the Program
https://www.youtube.com/watch?v=c0Gc1_gUxTg ( Part-1)
https://www.youtube.com/watch?v=nTXkq17_5O4 (Part-2)
Links to Previous AKR Memorial Lecture
3rd AKR Memorial Lecture (April 17th 2021)
2nd AKR Memorial Lecture (Jan 5th 2019)
1st AKR Memorial Lecture (Jan 7th 2017)
2. The Indian Physics Association in collaboration with the School of Astrophysics ,Presidency University presents the Second PAVINARI Lecture
Speaker: Dr. Suchetana Chatterjee, Presidency University
Time: 2 PM PC Mahalonobis Auditorium, 10.1.23
Title: Harvard's Computers: The Legacy of the Stellar Women
https://www.youtube.com/watch?v=NdQoCPcBd5E
1. Under the banner of the National Space Science Symposium-2022, Presidency University presents Outreach in the mother tongue (Convener: Dr. Suchetana Chatterjee, PU NSSE Coordinator, School of Astrophysics)
Outreach program for School students in Bangla, Dec 7th, Presidency Booth, Science City Kolkata
https://www.youtube.com/watch?v=L92DuMfXScM
https://www.youtube.com/watch?v=EFGUtLaPQGQ
Bangla Public Lecture by Prof. Somak Raychaudhuri, Dec 9th, 2022, Derozio Hall, Presidency Universityhttps://www.youtube.com/watch?v=qUPSmSPixcY
https://photos.app.goo.gl/SqbZx7WhT4irKBmi9
Wednesday Weekly Colloquium
Wednesday Weekly Colloquium
87. Colloquium at the School of Astrophysics:
Speaker: Prof. Nayana Majumdar, SINP.
Title: Muography with Cosmic Muons
Date, Time & Venue: Sept 10, 2:45 PM, Astrophysics Classroom 1.
Abstract: Muography is a non-invasive imaging technique that uses naturally occurring cosmic muons to probe the internal structures and composition of static objects. It has acquired significant attention in recent days for its diverse application in the field of science and technology. By measuring the flux and direction of muons as they pass through a target object, density mapping and muon deflection quantification can reveal inherent features and materials. Applications range from mapping unknown tombs and studying magma chambers to monitoring civil structures, nuclear waste, and contraband nuclear elements for homeland security. The scope and progress of research and development activities related to the societal application of muography in the Indian scientific and technological perspective will be discussed in the presentation.
86. Special Interdisciplinary Colloquium at the School of Astrophysics:
Speaker: Oindrila Raychaudhuri, Consultant Archivist, TIFR, Mumbai.
Title: Importance of Setting up Institutional Archives
Date, Time & Venue: Aug 27, 2:45 PM, A. K. Basak Auditorium.
Abstract: Every organization/institution creates records in the form of documents, letters, notices, photos etc. since its inception. These records are of utmost importance as they provide first-hand information or evidence relating to the history of that organisation. The need of preserving such records for posterity has been realised by many institutions and thus the idea of creating archives was born. The significance of archives lies in their ability to safeguard and provide access to these valuable documents.
This talk will first introduce the concept and principles of archives, and briefly discuss the procedure of how to set up an archive. This will be followed by an introduction to the idea of reconstructing the past through oral histories. Finally, after a brief introduction to the archives of the Tata Institute of Fundamental Research (TIFR), the talk will conclude with some snippets from the TIFR Archives, which will include information related to the beginning of the space program and the early history of radio astronomy in India.
85. Colloquium at the School of Astrophysics:
Speaker: Dr. Koustav Chandra, Penn State University, USA.
Title: GW231123: A "Shape-Shifting" Black Hole Merger that Spans the Pair-Instability Mass Gap
Date, Time & Venue: Aug 20, 2:45 PM, Astrophysics Classroom 1
Abstract: It has been nearly a decade since the first detection of gravitational waves from a binary black hole merger — a landmark event that ushered in a new era of astrophysics. While most events since then have been rather "uneventful", nature occasionally throws us a puzzle. GW231123 is one such event: a massive binary black hole merger with an estimated total mass between 190 and 265 solar masses, whose properties appear to shift depending on how we model the signal. One black hole seems to lie within, or even above, a theoretically forbidden mass range — the so-called pair-instability mass gap — while the other straddles it. Given its mass, most of GW231123’s signal power lies in the post-merger phase, making it a rare candidate for black hole spectroscopy and tests of strong-field dynamical gravity. In this talk, I will tell the story of this signal: how we detected it, why it is so perplexing, and what it might teach us about the lives (and deaths) of massive stars, the nature of black hole formation, and the pressing need for more robust and accurate waveform models.
84. Colloquium at the School of Astrophysics:
Speaker: Prof. Dhrubaditya Mitra, NORDITA, Stockholm, Sweden
Title: Written Out on Air and Running Water
Date, Time & Venue: Aug 13, 2:45 PM, Astrophysics Classroom 1
Abstract: Waves in air and water appear in physics at every level, from elementary to advanced. In this talk, I shall introduce waves in the Sun. To the crudest approximation, the Sun is a ball of gas. It is possible to observe traveling waves on the surface of the Sun by modern satellites. A theory of such waves starts with atmospheric waves in the earth's atmosphere which were first described by Horace Lamb [1]. Generalizing this to the Sun, it is now a routine exercise to infer the large-scale flow inside the Sun from the waves on its surface by solving an inverse problem. I shall give a general introduction to this subject, show the key steps to obtain the Lamb oscillations and hint on how to generalize it to the Solar plasma which also has magnetic field [2].
References:
[1] Lamb, Horace. "On atmospheric oscillations." Proceedings of the Royal Society of London, 1911.
[2] Tripathi, B and Mitra D. "Anisotropic Magnetized Asteroseismic Waves" The Astrophysical Journal, 2024.
83. Colloquium at the School of Astrophysics:
Speaker: Prof. Atreyee Sinha, TIFR, Mumbai, India
Title: The Universe at the Highest Energies: Results and Future Prospects from Ground-Based Gamma-Ray Astronomy
Date, Time & Venue: August 6th, 2:45 PM, Astrophysics Classroom 1
Abstract: In this talk, we'll explore the universe's most powerful particle accelerators through the lens of gamma rays, which act as cosmic messengers. We'll start by explaining how ground-based telescopes like the H.E.S.S. array detect these high-energy photons and how modern software like Gammapy helps us analyze the data. We'll then share exciting recent discoveries, including a new pulsar wind nebula, a glowing molecular cloud, and the extended gamma-ray halo around the Geminga pulsar. These findings are shedding light on how cosmic rays are accelerated and travel through our galaxy. We'll wrap up by looking at the future of gamma-ray astronomy with new observatories like the Cherenkov Telescope Array (CTAO) and India's own MACE telescope, highlighting the continued growth of this field.
SEMESTER BREAK
82. Colloquium at the School of Astrophysics:
Speaker: Prof. Suratna Das, Ashoka University, Sonipat, Haryana.
Title: Some "Background Checks" for Warm Inflation
Date, Time & Venue: April 30, 2:45 PM, Astrophysics Classroom 1
Abstract: Warm Inflation (WI) is a variant inflationary scenario where the inflaton field continuously dissipates its energy to a subdominant radiation bath during inflation. Among the many advantages that WI has over its more standard counterpart, which we will refer to as Cold Inflation, is that WI smoothly transits to a radiation dominated universe post inflation without invoking the need of a reheating phase, dynamics of which is still quite unknown. The dissipation effects effective during Warm Inflation makes the dynamics of the inflation quite intricate. Even the simple graceful exit in Cold Inflation turns out to be not so simple in Warm Inflation. In this talk, we will do the background analysis of Warm Inflation and shed light on how Warm Inflation ends or gracefully exits. These graceful exit criteria also constrain the form of the potential and the dissipative coefficients that one may choose for their Warm Inflationary model. Moreover, it indicates whether Warm Inflation can at all exit to a radiation dominated epoch or not.
81. Colloquium at the School of Astrophysics:
Speaker: Prof. Anirban Kundu, Calcutta University
Title: The Higgs Boson and Some Unanswered Questions
Date, Time & Venue: April 23, 2:45 PM, Astrophysics Classroom 1
Abstract: The Higgs boson, predicted in 1964 and discovered in 2012, is the lynchpin of our present understanding of particle physics. After a brief summary of what we already know, I will try to focus upon some rough edges --- things that tell us that all we know is at the most an incomplete story. These edges cover a wide spectrum --- from theoretical shortcomings to the physics of the early universe. I will not provide any solutions, as none are known. This will be a pedagogic talk aimed at the Master's as well as fresh PhD students.
80. Colloquium at the School of Astrophysics:
Speaker: Prof. Suvendu Rakshit, Aryabhatta Research Institute of Observational Sciences, Nainital.
Title: Unveiling the Cosmic Beasts: the Sub-Parsec Region of Active Galactic Nuclei
Date, Time & Venue: April 16, 3:30 PM, Astrophysics Classroom 1
Abstract: Active galaxies are believed to be powered by the accretion of matter onto supermassive black holes. Measuring the masses and investigating the dynamics within the sub-parsec region of active galactic nuclei (AGN) remains challenging due to the need for high spatial resolution. Long-term spectro-photometric monitoring has been a crucial tool for probing the central engine, determining the linear size of the broad-line region (BLR), and estimating black hole masses. Concurrently, recent advances in optical spectro-interferometry have provided an independent method to measure black hole masses by determining the angular size of the BLR. By combining the linear size obtained from spectro-photometric studies with angular diameter measurements from optical interferometry, we can estimate distances to AGN across the Universe. In this talk, I will summarize the results of extensive spectro-photometric monitoring programs conducted over several years, highlight the latest findings from optical interferometric observations, and discuss their implications for distance measurements to AGN.
79. Colloquium at the School of Astrophysics:
Speaker: Dr. Sibasish Laha, NASA Goddard Space Flight Center.
Title: Multi-Wavelength Observations of the Emergence of a Radio Jet in Real Time from a Supermassive Black Hole System.
Date, Time & Venue: April 11, 2:00 PM, P. C. Mahalanobis auditorium.
Abstract: An international team of scientists led by NASA Goddard Space Flight Center has discovered the formation of a powerful radio jet from the near vicinity of an active supermassive black hole (SMBH). Active SMBHs accrete matter very fast. In that process they emit huge amounts of radiation spanning almost the entire electromagnetic spectrum and jets containing high energy particles, and are known as active galactic nuclei (AGN). Although radio jets are detected in almost 10% of AGNs, this is one of the first instances in the history of astronomy that scientists have been able to observe a radio jet to form and evolve in real time. They also observe a unique "heart-beat" in X-rays while the jet is being formed. The X-rays are emitted from regions near the black hole event horizon, and detecting a quasi-periodic-oscillation (heart-beat) in the X-ray variability can provide crucial information about the jet formation and black hole behavior in these complex systems.
78. Colloquium at the School of Astrophysics:
Speaker: Dr. Shouvik Roychoudhury, Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), Taiwan.
Title: Cosmology in an extended parameter space: new constraints on dark energy and neutrino masses with DESI BAO.
Date, Time & Venue: April 02, 2:45 PM, Astrophysics Classroom 1
Abstract: We update constraints on cosmological parameters in a 12-parameter model, which extends the standard 6-parameter ΛCDM to include dynamical dark energy and massive neutrinos, along with other new parameters. We use the latest Planck PR4 (2020) likelihoods, DESI DR1 BAO, and the latest uncalibrated type Ia Supernovae (SNe) datasets. In this talk, I will discuss the implications for dynamical dark energy in such an extended model, and at the same time, provide robust bounds on neutrino masses which will be useful for the astro- and particle physics communities. I will also discuss the current status of the weak lensing tension and the Hubble tension in this extended cosmology. (Based on arXiv: 2409.13022; Published in ApJ Letters).
77. Colloquium at the School of Astrophysics:
Speaker: Prof. Archan S. Majumdar, S. N. Bose National Centre for Basic Sciences, Kolkata.
Title: Universe with large-scale inhomogeneities: cosmological evolution and gravitational wave propagation
Date, Time & Venue: March 26, 2:45 PM, Astrophysics Classroom 1
Abstract: The evolution of our Universe is well-described by the $\Lambda$CDM concordance model. However, in the present age of precision cosmology, several discordant observations have cropped-up. Although homogeneity and isotropy form the basis of the standard cosmological model, recent observations indicate the presence of inhomogeneities at very large scales with observed structures even at 500 ($h^{-1}$) Mpc. We explore the consequences of such inhomogeneities on cosmological evolution. In particular, we consider backreaction effects due to spatial averaging over inhomogeneities in the context of the Buchert model. Backreaction causes the departure from standard Hubble evolution at late times, leading to future deceleration and possible avoidance of the big-rip problem for the currently accelerating Universe. Backreaction from matter inhomogeneities further predicts a dip in the 21-cm brightness temperature. We finally consider the propagation of gravitational waves from compact binaries in the Universe with large-scale inhomogeneities. We show how modifications to the redshift-dependent gravitational wave amplitude may significantly impact precise estimation of the binary parameters.
76. Colloquium at the School of Astrophysics:
Speaker: Prof. Sudipta Das, Visva-Bharati.
Title: Exploring the Cosmos: Peering into the Dark Side of the Universe
Date, Time & Venue: March 19, 2:45 PM, Astrophysics Classroom 1
Abstract: The universe is a vast and mysterious expanse, much of which remains hidden from our direct observation. While luminous matter—stars, galaxies, etc. showcase a dazzling view of the Universe, a significant portion of the universe exists in darkness. This talk will explore the enigmatic “dark side” of the cosmos, encompassing the dark components, namely, dark matter and dark energy and their roles in shaping the evolution of the Universe. We will particularly discuss the perplexing nature of dark energy, the force driving the accelerated expansion of the Universe, and how cutting-edge telescopes and cosmological surveys aim to decode its properties. By combining theoretical insights with observational breakthroughs, we are gradually uncovering the unseen forces that govern the cosmos. This talk will provide an accessible yet in-depth look at these profound cosmic mysteries and the future directions in our quest to understand the dark side of the Universe.
75. Colloquium at the School of Astrophysics:
Speaker: Prof. Ananda Shankar Chowdhury, Department of Electronics and Telecommunication Engineering, Jadavpur University.
Title: Can You Recognize the Correct Patterns?
Date, Time & Venue: March 12, 2:45 PM, Astrophysics Classroom 1
Abstract: Automated recognition of correct patterns assume paramount importance in diverse spheres of life. In this talk, I will show how computer vision algorithms empowered with machine and deep learning can recognize correct patterns from images and videos. Two example problems from very different domains, namely, medical imaging, and surveillance will be discussed. In the first problem, segmentation of tumors from MRI images of human brain will be addressed. We will demonstrate how a combination of deep learning and graph cuts can successfully achieve this task in the presence of intensity homogeneity and noise. The second problem is on open-set person re-identification. The problem of basic (close-set) person re-identification deals with identifying target persons across non-overlapping views with the assumption that a probe image is contained in a set of gallery images (video frames). However, in typical long duration videos, there is no such guarantee which makes the open-set re-identification problem extremely challenging. We will show how a joint optimization of the Weibull distribution and the Mahalanobis metric in the framework of Large Margin Nearest Neighbor can fulfill this goal.
74. Colloquium at the School of Astrophysics:
Speaker: Prof. Asis Kumar Chattopadhyay, Interdisciplinary Statistical Research Unit, Indian Statistical Institute, Kolkata (Former Professor, Department of Statistics, University of Calcutta)
Title: Statistical Investigation of Star Formation Rate in Galaxies in the Local Volume
Date, Time & Venue: March 05, 2:45 PM, Astrophysics Classroom 1
Abstract: We have concentrated on application of statistics to astronomy and the development of statistical methods to solve various problems related to the Universe, leading us to discoveries of new astrophysical phenomena. We often get data that are contaminated with noise, influenced by outliers or sparsely distributed. In all such situations, the usual statistical methods fail and we need to use their adaption or to introduce new methods as per requirements. In this talk, we concentrate on a particular problem on star formation. Star formation scenario in galaxies of various morphological types is significant in a sense that it characterizes the structure formation in the Universe. But direct measurement of SFRtrue (True values of SFR) is not at all possible as one has to count stars formed per year in a galaxy accurately. In this work the star formation is investigated by the Gaussian Mixture Model Based Clustering (GMMBC) technique to form the clusters of galaxies using a large data set of galaxies in the Local Volume (LV).
73. Colloquium at the School of Astrophysics:
Speaker: Dr. Agniva Roychowdhury, Space Telescope Science Institute, USA.
Title: Unraveling the Nature of Extragalactic Jets with Radio Interferometry
Date, Time & Venue: February 19, 2:45 PM, Astrophysics Classroom 1
Abstract: While extragalactic jets have been studied for more than half a century now, various open questions and uncertainties about their true physical nature still plague us. Using the techniques of radio interferometry and electrodynamics, this talk will discuss the intricacies in theory and observations of jets from active galactic nuclei. Jets have complex structure and dynamics, the nature of which differ through the spatial scales being probed. Understanding of the exact physics is sensitive to both the accuracy of the observations and the accuracy of the relevant interpretations. This talk will aim to reduce part of the prevailing uncertainties by using examples of observations of jets using the Very Large Array and the Very Large Baseline Array both, and will supplement them by novel findings of jet dynamics and acceleration/deceleration, achieved using radio interferometric techniques.
72. Colloquium at the School of Astrophysics:
Speaker: Prof. Indranil Chattopadhyay, ARIES, Nainital.
Title: On Disk Formation around Isolated Black Holes via Stream Accretion
Date, Time & Venue: February 12, 2:45 PM, Astrophysics Classroom 1
Abstract: We investigate accretion onto an isolated black hole from uniform winds. If the winds are directed towards the black hole, then the accretion process can be well described by the classical Bondi-Hoyle Lyttleton or BHL accretion. If the wind is not directed towards the black hole and flows past it, then a smaller fraction of the flow can be attracted by the black hole, and this type of accretion cannot be described by the classical BHL, and we coin the second kind as the lateral BHL. We show that the classical BHL cannot form an accretion disk, while lateral BHL can form transient accretion disks. To describe the thermodynamics of the flow, we have used a variable adiabatic index equation of state which depends on the temperature of the flow as well as the composition of the gas. We show that the electron-proton gas forms an accretion disk, which disappears and forms a shock cone, only to form the disk again at a later time, while for flows with less protons, the accretion disk, once lost, does not reappear again. Only when the flow is pair-dominated does it form a persistent accretion disk. We also show that a shock cone is less luminous than the accretion disk.
71. Colloquium at the School of Astrophysics:
Speaker: Dr. Gourav Banerjee, Indian Institute of Astrophysics, Bengaluru.
Title: Study of Stellar Gaseous Discs: An lndian Odyssey
Date, Time & Venue: February 05, 2:45 PM, P. C. Mahalanobis Auditorium
Abstract: Gaseous stellar discs are a rare natural phenomenon, which provide insights about how gas particles behave at extreme temperatures. Classical Be stars, exotic rapidly rotating, main sequence stars do possess such type of discs, thus being accessible for studies using ground based observing facilities. Showing emission lines of different elements in their optical spectra, they provide excellent and the only natural laboratory to study stellar gaseous disc physics. India is currently one of the leaders in Be star research, led by teams from IIA and CHRIST (Deemed to be University), Bangalore. I shall be highlighting the basics about Be stars, their astrophysical context and highlight the status and opportunities in Be star research in India and beyond.
70. Colloquium at the School of Astrophysics:
Speaker: Prof. S. Raj Chaudhury, University of South Alabama, USA.
Title: Learning Science and the Science of Learning
Date, Time & Venue: 29 January 2025, 2:45 PM, Astrophysics Classroom 1.
Abstract: In this talk, we shall explore together a thread that binds my work in studying the teaching and learning of science and the role of instructional faculty in navigating applicable lessons from the learning sciences. I have been inspired by the work of physicist Fred Reif, Carnegie Foundation presidents Ernest Boyer and Lee Shulman as well as cognitive psychologist John Bransford. While all these names may not be familiar, I hope to share with you my synthesis and perspective of different ways in which their work contributes to how we can think of our roles in academia as teachers and scholars. We shall touch upon the nature of expertise, how expertise is valued in academia and time permitting, an application of a well known active learning exercise in physics – the Interactive Lecture Demonstration (much physics knowledge not a prerequisite). This talk is appropriate for students, faculty and staff from all disciplines who are interested in research informed approaches to teaching and learning. I will not share any new physics, but my hope is that you will leave with some new ideas to frame your thinking about teaching and learning in higher education.
69. Colloquium at the School of Astrophysics:
Speaker: Dr. Anarya Ray, Northwestern University, USA.
Title: Exploring the Universe with Gravitational Waves: How do Binary Black Holes Form?
Date, Time & Venue: 22 January 2025, 2:45 PM, Astrophysics Classroom 1.
Abstract: Gravitational waves (GWs) from compact binary mergers have opened up a new window to the Universe. In the era of growing GW catalogs, new insights into several mysteries of modern physics are imminent. The novel information carried by GWs is often complemented and significantly enhanced by the detection of their multi-messenger counterparts.
In the first part of my talk, I will briefly introduce the scientific potential of growing GW catalogs and multi-messenger observations in elucidating the uncertainties that persist in our current understanding of compact binary formation, the nature of the cosmological expansion, and the very nature of fundamental interactions. I will also quickly highlight the exciting opportunities in GW astronomy that lie ahead for interested early career scientists in the context of these investigations.
In the second half of my talk, I will focus in more detail on one of the aforementioned explorations, namely that of the origin of merging stellar-mass binary black holes (BBHs). In particular, I will talk about how data-driven population analysis methods can extract insights into the fundamental astrophysical processes that underlie BBH formation. I will show some new results we obtained from the third gravitational wave transient catalog, their implications on BBH formation, and the next steps in the context of ongoing and future observing runs of current GW detectors. I will then conclude with a brief mention of extending our current work to delve deeper into the mysteries of BBH formation and the role to be played by machine learning in the realization of such endeavors.
68. Colloquium at the School of Astrophysics:
Speaker: Dr. Pritam Palit, Carnegie Mellon University, USA.
Title: The Light Dark Matter Experiment (LDMX).
Date, Time & Venue: 8 January 2025, 12 PM, Astrophysics Classroom 1.
Abstract: The constituents of dark matter are still unknown, and the viable possibilities span a very large mass range. Specific scenarios for the origin of dark matter sharpen the focus on a narrower range of masses: the natural scenario where dark matter originates from thermal contact with familiar matter in the early Universe requires the DM mass to lie within about an MeV to 100 TeV. Considerable experimental attention has been given to exploring Weakly Interacting Massive Particles in the upper end of this range (few GeV – ~TeV), while the region ~MeV to ~GeV is largely unexplored. Most of the stable constituents of known matter have masses in this lower range, tantalizing hints for physics beyond the Standard Model have been found here, and a thermal origin for dark matter works in a simple and predictive manner in this mass range as well. It is therefore an exploration priority. If there is an interaction between light DM and ordinary matter, as there must be in the case of a thermal origin, then there necessarily is a production mechanism in accelerator-based experiments. The most sensitive way (if the interaction is not electron-phobic) to search for this production is to use a primary-electron beam to produce DM in fixed-target collisions. The Light Dark Matter eXperiment (LDMX) is a planned electron-beam fixed-target missing-momentum experiment that has unique sensitivity to light DM in the sub-GeV range. This talk will give an overview of the theoretical motivation, the main experimental challenges and how they are addressed, as well as projected sensitivities in comparison to other experiments.
SEMESTER BREAK
67. Colloquium at the School of Astrophysics:
Speaker: Prof. Daisuke Nagai, Yale University, USA.
Title: Cosmology in the Era of Multi-Wavelength Surveys.
Date, Time & Venue: 27th November, 2024, 11 AM, A.K. Basak Auditorium.
Abstract: We are entering the golden age of multi-wavelength astronomical surveys. In the 2020s, a plethora of surveys (such as Euclid, eROSITA, Rubin-LSST, Simons Observatory, and CMB-S4) are underway or planned to provide unprecedented insights into cosmology and galaxy formation. In this talk, I will discuss the significant scientific opportunities and challenges that arise in the era of big data, highlighting recent advances in computational modeling and the critical roles played by artificial intelligence and machine learning.
No colloquium: ''শতবর্ষে বোস পরিসংখ্যান তত্ত্ব" 100 years of Bose Statistics at A. K. Basak auditorium, PU. Date: 20-Nov-2024 (Wednesday)
66. Colloquium at the School of Astrophysics:
Speaker :Dr. Trisha Bhowmik, Universidad Diego Portales, Santiago, Chile.
Title: The Ophiuchus Disc Survey Employing ALMA (ODISEA): A study of Planet-Forming Disks.
Date and Time: 13th November, 2024, 02:45 PM at Astrophysics Classroom I.
Abstract: Our solar system differs between terrestrial and giant planets regarding their architecture and chemistry. We need to look at the planet-forming disks and their architectural variation to understand this difference. As part of the ODISEA project (Ophiuchus DIsk Survey Employing ALMA), I will present 55 faint disks at 0.05” (7 au) resolution and 45 brighter disks at 0.2” (28 au) resolution in 400 GHz. This study measures the size distribution of 100 disks in a single molecular cloud (at < 200 pc) for the very first time to investigate how disk substructures evolve as a function of disk size, mass, and SED Class from their radial profiles. We expect that there will be a higher population of young (≤ 1Myr) featureless disks than evolved (a few Myr) featureless disks. However, we see an ambiguity of a similar population of embedded and Class II featureless disks. A possible scenario could be the presence of pressure bumps that can halt grain growth and consequently structural evolution in the disks.
Diwali Break (31.10.24-10.11.24)
65. Colloquium at the School of Astrophysics:
Speaker :Prof. Amitabha Lahiri, S.N.Bose National Centre for Basic Sciences, Kolkata
Title: Solar Neutrino Problem and Neutrino Oscillation.
Date and Time: 30th October, 2024, 02:30 PM at Astrophysics Classroom I
No Colloquium: Prof. Kulesh Chandra Kar 125 years celebration : Special Lecture by Prof. Arnab Rai Choudhuri , IISc
Autumn Break (5.10.24-20.10.24)
64. Colloquium at the School of Astrophysics:
Speaker :Dr. Tathagata Saha, Leibniz Institute for Astrophysics, Potsdam, Germany.
Title: Morphology of Accreting Gas in Active Galactic Nuclei: Heavy Obscuration and Extreme Variability.
Date and Time: 25th September, 2024, 02:30 PM at Astrophysics Classroom I
Abstract:
Significant challenges remain in understanding the morphological properties of heavily obscured AGNs and conditions of extreme spectral and time variability in active galactic nuclei (AGNs). I discuss the current knowledge and challenges in constraining the obscuring torus properties in heavily obscured AGNs and mechanisms triggering extreme variability. Multiple X-ray spectral models have been developed to study the X-ray spectral properties of the obscuring AGN torus. It is suspected that these models are degenerate with each other at the current X-ray data quality. To investigate these effects, we simulate data in the context of the models and use Bayesian methods to analyze them. The first part of the talk demonstrates the consequences of applying a correct or wrong torus model (with implications on the torus morphology determination) and the robustness of parameter estimates (with impact on calculated parameter precision). Several AGNs exhibit variability in excess (factor>10) of the regular AGN variability. These sources also exhibit a Seyfert-type change and are called changing look AGNs (CLAGN). In the second part of the talk, I present the results of our multi-wavelength campaign of two X-ray and optically selected CLAGNs, which are variable at dissimilar timescales. We study the response of the inner accretion flow, BLR, and the parsec-scale dust structure and the trigger of these events in the context of accretion flow instability.
63. Colloquium at the School of Astrophysics:
Speaker :Dr. Dhrubojyoti Sengupta, University of Maryland, Baltimore County, USA.
Title: X-ray Vision on Local Obscured Active Galactic Nuclei.
Date and Time: 18th September, 2024, 12:30 PM at Astrophysics Classroom I
Abstract:
Most of the Cosmic X-ray Background (CXB) radiation from 1-100 keV is the result of AGN emission. The contribution from the unobscured AGN population, responsible for the CXB emission at <10 keV, has been almost completely resolved. However, the detection of obscured AGN, which are responsible for a significant fraction (~40% at peak) of the CXB, is found to be challenging. By observation, the obscured Compton-Thick (CT: column density >10^24 /cm^2 ) AGN fraction in the local universe is (10-50)% lower than that expected from CXB population synthesis models. Therefore, an almost complete census of obscured AGN is needed at different wavelengths to fill the gap between observations and model predictions. It is commonly accepted that the nuclear obscuration in an active galaxy (at least at low redshift) is caused by the circum-nuclear material of molecular and dusty clouds called "torus", but its geometrical, physical, and chemical properties are far from being accurately known. In this talk, I will present a comprehensive and systematic analysis of a sample of few local obscured AGN candidates (z<0.05) through X-ray spectral analysis using Chandra and XMM-Newton at E<10 keV, coupled with NuSTAR data at E>10 keV, to characterize the torus obscuration. The purpose is to update the census of CT-AGN by studying the different properties of the torus over the energy range 0.3-50 keV using physically motivated torus models like- MyTorus, borus02, UxClumpy, Xclumpy. Adding our analysis to the previous results, we find the total population of local CT-AGN almost reduces to half when using NuSTAR observation. We also find around 78% of the population shows a clumpy nature of torus. I will also briefly mention a self-consistent multi-wavelength analysis, i.e. a joint analysis combining the mid-IR SED-derived view of the obscuring medium with that from X-rays, using X-CIGALE.
62. Colloquium at the School of Astrophysics:
Speaker : Dr. Arghajit Jana, FONDECYT Fellow, Universidad Diego Portales, Santiago, Chile.
Title: Changing-Look AGN: Challenging Our Understanding of Active Galactic Nuclei.
Date and Time: 7th Aug, 2024, 2:30 PM at Astrophysics Classroom I
Abstract:
The changing-look active galactic nuclei (CLAGN) switches between type-1 and type-2 spectral state. The rapid transition can not be explained by the unification model of AGNs, which has been used to explain the AGN phenomenon over four decades. The reason for the CL transition is still unclear and subject to active research. We discuss our current understanding, challenges and future prospects of such objects in this talk.
61. Colloquium at the School of Astrophysics:
Speaker : Prof. Dipankar Maitra, Wheaton College, Massachusetts, USA.
Title: Doing Exciting Science with (Relatively) Small Telescopes: Probing the Extreme Environment near the Black Hole X-ray Binary V404 Cygni.
Date and Time: 31st July, 2024, 2:30 PM at Astrophysics Classroom I
Abstract:
I will present some results that show how interesting science can be carried out using small telescopes if you are at the right place at the right time. Specifically, I will present optical observations of the black hole X-ray binary system V404 Cygni obtained using Wheaton College’s 12-inch telescope. The correlated multi-wavelength flux variability that we observed, along with flux ratios between different filters, suggest that the optical emission originated very close to the black hole, in a 'jet' outflow moving at relativistic speeds. Our data, in conjunction with simultaneous data obtained by space-borne missions such as INTEGRAL and Swift, strongly suggest that the launching region of this jet was extremely compact and energetic compared to other X-ray binary systems observed so far.
60. Colloquium at the School of Astrophysics:
Speaker : Dr. Manami Roy, CCAPP Fellow, Ohio State University, USA.
Title: Unveiling the Complex Temperature Structure of the Galactic Halo.
Date and Time: 10th July, 2024, 2:30 PM at Astrophysics Classroom I
Abstract:
The circumgalactic medium (CGM), the gaseous halo enveloping galaxies, plays a crucial role in shaping the evolution of galaxies by providing the fuel for star formation. This medium is multiphase and exhibits a vast temperature structure, ranging from the cool 10^4 K gas to super-virial 10^7 K gas. The presence of the cool gas in the outer CGM presents intriguing questions, as does the enigmatic location of the newly discovered super-virial gas. In this talk, I aim to shed light on these two enigmas by leveraging simulations and observational studies.
59. Colloquium at the School of Astrophysics:
Speaker : Prof.Surajit Sen, Professor of Physics, SUNY Buffalo & Honorary Consultant, Swanirvar, Andharmanik, N 24 Pgns, West Bengal.
Title: Can we empower the 3 billion youth of the developing world?
Date and Time: 27th June, 2024, 2:00 PM at Astrophysics Classroom I
Abstract:
As a Jefferson Science Fellow of the US National Academies, I served as a Senior Science Advisor at the US Agency for International Aid in 2020-2021. An area I focused on while at USAID was to see how development problems are being addressed "on the ground." It was easy to see that the world of different fields, specializations, etc. melted away when trying to solve even the simplest of issues, e.g., how to make sure we can educate a group of kids and ensure they attend school and remain engaged. The socio-economic, energy, mental health, cultural, etc. problems were all inseparably entangled, the solutions were inevitably emergent. In a way these are true complex systems. I will try to give a flavor of my on the ground involvement in development space in this real complex system.
58. Special Colloquium at the School of Astrophysics:
Speaker : Prof. Arka Banerjee, IISER, Pune.
Title: Extracting maximal information from cosmological surveys: The role of summary statistics
Date and Time: 12th June, 2024, 2:30 PM at Astrophysics Classroom I
Abstract:
As cosmological surveys continue to provide exquisite data about our Universe across various wavelengths, a crucial question to ask ourselves is how to use this data to answer the major questions in cosmology - the origin and fate of the Universe, the various components that make up the Universe, and their micro physical description. This is typically done by compressing petabytes of original data into effective “summary statistics” that can be compared against theoretical predictions. More informative summaries of the data allow us to better constrain theoretical models using the same original data. In this talk, I will introduce and discuss the advantages and drawbacks of various summary statistics that have been extensively used in the literature - such as N-point functions, 1-point PDFs, and Minkowski Functionals. I will then introduce a novel and extremely useful summary statistic - the k-Nearest Neighbor (kNN) distribution. I will show its current applications to various cosmological datasets, outperforming inferences using other summary statistics. I will then show how the kNN framework is ideally suited to connect the disparate languages of the other existing summary statistics - thereby allowing for a thorough quantitative study of the relative information content in them. Finally, I will end with some directions in AI/ML that are being discussed in this context.
SEMESTER BREAK
57. Colloquium at the School of Astrophysics:
Speaker : Prof. Subhasish Banerjee, Ashoka University.
Title: Ethics of Data-Driven Models and AI/ML.
Date and Time: 3rd May, 2024, 3 PM at P. C. Mahalanobis auditorium.
Abstract:
In this talk we will examine some ethics considerations in purely data-driven predictive analytics applications. In the first part of the talk we will discuss the issues that arise due to possible unreliability of data-driven analytics models when deployed in the wild. In the second part of the talk we will examine the risks in automating decisions about people, particularly those related to the possibilities of bias, unfairness and discrimination.
56. Colloquium at the School of Astrophysics:
Speaker : Dr. Bidisha Bandyopadhyay, Universidad de Concepción, Chile.
Title: Peeping close to the horizons of supermassive black holes in the heart of AGN.
Date and Time: 3rd April, 2024, 2.30 PM at Astrophysics Classroom.
Abstract:
Active galactic nuclei (AGN) are the most powerful and brightest sources in the Universe which are believed to be driven by the accretion mechanism around the supermassive black hole at the center of these systems. With the improvement in very long baseline interferometry (VLBI) technology and facilities such as the Event Horizon Telescope, it has now been possible to probe regions close to the horizon scale of two supermassive black holes, one in the Virgo cluster (M 87) and the other in the heart of our Galaxy (Sgr A*). In this talk, I will be discussing the accretion and emission mechanism close to the horizon scale of such systems. Further it will also be discussed how to extract various emission features with current high resolution facilities or with future Earth-space based VLBI facilities.
55. Colloquium at the School of Astrophysics:
Speaker : Dr. Arka Chatterjee, University of Manitoba, Winnipeg, Canada.
Title: Painters of X-ray Light Curves and Spectra from Black Holes: Origin of X-Ray Soft Lag.
Date and Time: 20th March, 2024, 2.30PM at Astrophysics Classroom.
Abstract:
During accretion onto a black hole, matter experiences an extreme gravitational and thermodynamic environment. Understanding accretion onto Galactic black holes relied on the studies of the X-ray light curves and spectra collected by the space telescopes during the past five decades. The light curves are gathered by telescopes, where photon counts are stored with respect to their energy and time. They often contain quasi-periodic oscillations (QPOs) and exhibit time delays and lags between the energy bands. The X-ray spectra, on the other hand, contain energy information and photon counts. In the first part of the presentation, we will address how the major players of accretion shape the light curves from sources containing a black hole. Then, we will uncover how those players modify their broadband X-ray spectra and light curves. Finally, we will discuss possible scenarios causing the elusive soft X-ray lag in Galactic black holes.
54. Colloquium at the School of Astrophysics:
Speaker : Prof. Bharat Ratra, Kansas State University, USA
Title: Spatial Curvature, Dark Energy Dynamics, Neither, or Both.
Date and Time: 11th March(Monday), 2024, 11.00AM @ P C Mahalanobis Auditorium.
Abstract:
Observations over the last two decades have persuaded cosmologists that (as yet only indirectly detected) dark energy is by far the main component of the energy budget of the current universe. I review a few simple dark energy models and compare their predictions to observational data, to derive dark energy model-parameter constraints and to test consistency of different data sets. I conclude with a list of open cosmological questions.
53. Colloquium at the School of Astrophysics:
Speaker : Prof. Sudip Bhattacharyya, TIFR, India.
Title: Continuous Gravitational Waves from Spinning Neutron Stars.
Date and Time: 5th March(Tuesday), 2024, 3.30PM @ School of Astrophysics Classroom.
Abstract:
Neutron stars contain more than a solar mass within a 10-15 km radius. These superdense stars provide excellent opportunities to probe extreme aspects of physics, such as strong gravity, high magnetic field, accretion mechanism, high-density degenerate matter, and continuous gravitational waves, which cannot be studied in terrestrial laboratories. However, while gravitational waves, which are 'ripples' in space-time, have recently been detected from short-lived merger phenomena of black holes and neutron stars, continuous gravitational waves remain elusive. Nevertheless, such waves could be inferred from spin down rates of neutron stars. Here, we will show, using multi-wavelength observations, that the neutron star PSR J1023+0038 should have a permanent ellipticity and hence emits gravitational waves continuously.
52. Colloquium at the School of Astrophysics:
Speaker : Prof. Sourav Bhattacharya, Jadavpur University, Kolkata.
Title: Loops in Primordial Cosmic Inflation.
Date and Time: 28th February, 2024, 2.30PM @ School of Astrophysics Classroom.
Abstract:
In this talk, I wish to discuss the effect of fluctuations and loops of quantum fields during the primordial inflationary stage of our universe. During this stage, our universe underwent a very rapid, near exponential phase of accelerated expansion, often modeled as the de Sitter spacetime. I will first review some open challenges associated with understanding this era of our universe, including the celebrated cosmic coincidence puzzle. It turns out that massless but conformally non-symmetric interacting quantum fields (such as a massless minimal scalar, graviton) show non-perturbative growth of different amplitudes such as the self energy or correlation functions, at late times. These non-perturbative growths, known as the secular effect, are characterised by the powers of the logarithm of the scale factor. This indicates breakdown of perturbation theory at late times, necessitating resummation of associated loop diagrams. I will discuss how such resummation can yield observable effects in terms of the dynamical generation of the field mass. The results of a few recent works by our group in this regard will be briefly discussed. The possible connection of the secular effect with the aforementioned cosmic coincidence problem will be emphasised.
51. Colloquium at the School of Astrophysics:
Speaker : Dr. Pratik Tarafdar, Institute of Mathematical Sciences, Chennai.
Title: Tuning into 'Cosmic Hum': The First Hints of a Stochastic Gravitational Wave Background
Date and Time: 21th February 2024, 3:30 PM @ School of Astrophysics Classroom.
Abstract:
The first direct detection of gravitational waves was made by the LIGO-Virgo collaborations in 2015. Such spacetime ripples with wavelengths of the order of kilometres are generated during the final few milliseconds of stellar mass black hole or neutron star mergers, beyond which their strength falls below our present instrumental sensitivity. However, continuous gravitational wave emissions had been predicted in colliding galaxies from supermassive black hole binaries (SMBHB) revolving around each other for years before the ultimate merger. Superposition of such emissions from a large number of SMBHBs is expected to create a persistent stochastic gravitational wave background (SGWB) with wavelengths of the order of light years (in nano-Hz frequencies). Detection of such a background requires detectors with light-year arm lengths that cannot be achieved by ground-based or even the advanced upcoming space-based gravitational wave detectors. Thankfully, nature has gifted us ultra-precise galactic clocks placed light years apart named 'millisecond pulsars' as potential tools to detect these nanohertz gravitational waves. Recent results announced by the Indian Pulsar Timing Array (InPTA), the European Pulsar Timing Array (EPTA), the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), the Parkes Pulsar Timing Array (PPTA) from Australia, and the Chinese Pulsar Timing Array (CPTA), unravel the first strong direct hints of such a cosmic gravitational wave background.
50. Colloquium at the School of Astrophysics:
Speaker : Dr. Nazma Islam, NASA Goddard Space Flight Center, Greenbelt, USA.
Title: Exploring the Hot and the Energetic Universe
Date and Time: 7th February 2024, 3:30 PM @ School of Astrophysics Classroom.
Abstract:
High-energy electromagnetic radiation traces the hot and energetic phenomena occurring in the Universe. It probes the 'hot' gas in galaxies and clusters, as well as the 'energetic' accretion flows around compact objects and supermassive black holes. The key questions in astrophysics are related to understanding the nature of these accretion flows around compact objects and supermassive black holes, and how they influence the formation and evolution of large-scale structures like galaxies and clusters of galaxies. In this talk, I will present results from investigations into understanding the 'universal' nature of these accretion flows and how the feedback from them affects the distribution of hot gas in galaxies. Finally, I will mention future plans related to understanding these hot and energetic processes on different lengths and timescales in the era of multi-messenger astronomy.
No Colloquium: Jan 31st : ASI Meeting
49. Colloquium at the School of Astrophysics:
Speaker : Prof. Chandrachur Chakraborty, Manipal Centre for Natural Sciences, MAHE, Karnataka.
Title: Can we see a singularity, the most extreme object in the universe?
Date and Time: 17th January 2024, 3:30 PM @ School of Astrophysics Classroom.
Abstract:
When the fuel of a very massive star is spent, it collapses due to its own gravitational pull and eventually becomes a very small region of arbitrarily high matter density, that is a 'singularity', where the usual laws of physics may break down. If this singularity is hidden within an event horizon, which is an invisible closed surface from which nothing, not even light, can escape, then we call this object a black hole (BH). But if the event horizon does not form, we are left with the tantalizing option of observing a naked singularity (NS). An important question then is, how to observationally distinguish a NS from a BH. I shall show that the precession frequency of a gyroscope orbiting a BH or a NS is sensitive to the presence of an event horizon. A gyroscope circling and approaching a BH from any direction behaves increasingly 'wildly,' that is, it precesses increasingly faster, without a bound. But, in the case of a NS, the precession frequency changes by a small amount, in a regular well-behaved manner. I shall also show that the precession of orbits of matter falling (accretion) into a rotating BH or a NS can be used to distinguish these exotic objects. This finding could be used to distinguish a NS from a BH in reality, because the precession frequencies could be measured in X-ray wavelengths, as the infalling matter radiates X-rays. In fact, we have recently reported the first observational indication of gravitomagnetic monopole (gravitational analogue of Dirac's magnetic monopole) using the X-ray data from a star, collapsed into the most extreme object in the universe, a singularity.
48. Colloquium at the School of Astrophysics:
Speaker : Dr. Santanu Mondal, Indian Institute of Astrophysics, Bengaluru.
Title: Observational Aspects of Accreting Black Holes.
Date and Time: 10th January 2024, 3:30 PM @ School of Astrophysics Classroom.
Abstract:
Black holes are black, but material captured by their immense gravity forming a disk-like structure can be heated to extremely high temperatures as it approaches inward, resulting in powerful X-ray emission. The infalling material occasionally produces powerful jets from the inner region of the disk. The phenomenology of X-ray observations of these objects is very rich and has been exhaustively studied. To date, however, there is little agreement on the physics behind these accretion states. To go beyond the standard model of a stable accretion flow, with no corona and only a parametric viscosity of unknown origin, it is necessary to rely on a promising physical solution. In this talk, I will discuss how the spectral and temporal properties during the outburst phase of the black holes change and the role of cooling, viscosity, and jets/outflows in triggering them. Finally, I will touch upon my recent work on understanding the changing look phenomena in active galactic nuclei.
47. Colloquium at the School of Astrophysics:
Speaker : Dr. Minhajur Rahaman, Open University of Israel, Raanana.
Title: The Very Pulse of the Machine.
Date and Time: 10th January 2024, 12:30 PM @ School of Astrophysics Classroom.
Abstract:
Gamma-ray bursts (GRBs) are the brightest electromagnetic events in the Universe. Internal shocks are one of the prominent dissipation mechanisms for prompt phase of GRBs. In internal shocks, each collision between two shells forms a pair of forward and reverse shocks, which dissipate part of their kinetic energy into internal energy. The dissipation is governed by hydrodynamics. However, most studies in the literature treat this as a plastic collision of two infinitely thin shells without any reference to hydrodynamics. Starting from the basic properties of the central engine we derive the physical properties of the shells before and after their collision. The properties of the shocked regions are significantly different and imply interesting observable consequences such as different luminosities, peak times, and peak photon energies from these two shocked regions. In particular, we will show that the internal shock model can account for certain key features of the prompt gamma-ray spectra and the diversity of the light curves.
46. Colloquium at the School of Astrophysics:
Speaker : Prof. Debarati Chatterjee, Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune.
Title: Gravitational Wave Astronomy: A New Window to the Invisible Universe.
DateDate and Time: January 3rd 2024, 3.30 PM @ School of Astrophysics Classroom.
Abstract:
Compact stars are enigmatic objects in the Universe that challenge our understanding of Physics under extreme conditions of density, temperature, gravity, rotation and magnetic fields. However the correct interpretation of multi-wavelength astrophysical data of compact stars remains challenging, as it probes properties of matter beyond the realm of present terrestrial experiments, such as nuclear or heavy-ion experiments. A recent breakthrough emerged with the direct detection of gravitational waves from mergers of compact stars in binary systems. In this talk, I will elucidate how the discovery of gravitational waves has revolutionized astronomy as well as nuclear and particle physics by allowing us to probe the interior of compact objects.
45. Special Colloquium at the School of Astrophysics:
Speaker : Prof. Ranjan Laha, Indian Institute of Science
Title: Detecting low-mass primordial black holes as the dark matter candidate
Date and Time: 20th December, 2023, 3.30PM at P. C. Mahalanobis Auditorium.
Abstract:
The identity of dark matter is one of the biggest mysteries of science. Primordial black holes (PBHs) are one of the oldest and well-motivated dark matter candidates. PBHs can have a wide range in masses and their detection techniques vary (depending on their masses). I will be concentrating on the low-mass end of PBH masses (masses \sim 10^{16} g to 10^{18} g). I will discuss how one can detect the Hawking radiation from these objects. I will discuss the current constraints using various astrophysical observables like low-energy Galactic positrons, gamma-rays, and other observables. I will also discuss how near-future gamma-ray telescopes can discover low-mass PBH dark matter.
44. Special Colloquium at the School of Astrophysics:
Speaker : Prof. Mayukh Pahari, IIT Hyderabad
Title: Understanding the Innermost Geometry of Accreting Seyfert galaxies using X-ray Reverberation Techniques
Date and Time: Dec 20th 2023, 12 PM @ School of Astrophysics Classroom
Abstract:
Signs such as rapid X-ray fluctuations and significant variability in RMS values imply that the X-ray emitting source in an accreting supermassive black hole is nearest to the black hole. However, details regarding its size, shape, and precise position remain unclear, often linked to the base of the radio jet along the black hole's vertical spin axis. X-ray reverberation, a vital observation technique involving coronal X-rays reflecting off the inner accretion disc, indicates a delayed, modified emission. Interestingly, the time delay measurements from such a modified emission in UV and optical follow standard thin disc theory; however, X-ray departs. In this talk, I will discuss how X-ray reverberation observationally differs from other wavelengths and how the lamppost geometric configurations can be used to explain the measured X-ray reverberations in Seyfert galaxies.
43. Special Colloquium at the School of Astrophysics:
Speaker : Dr. Aritra Ghosh, University of Washington
Title: Investigating Galaxy Morphology in Large Surveys Using Novel Machine Learning Frameworks
Date and Time: Dec 19th 2023, 2 PM @ School of Astrophysics Classroom
Abstract:
The morphological features and structural parameters of galaxies have played an instrumental role in our understanding of galaxy formation and evolution. In this talk, I will outline how we have developed novel machine-learning frameworks that can determine the morphology of billion-galaxy samples expected over the next decade. We have used these frameworks to create one of the largest structural parameter catalogs currently available, containing ~8 million Hyper Suprime-Cam galaxies. This catalog represents a significant improvement in size (~10X), depth (~4 mag), and uncertainty quantification over current state-of-the-art bulge+disk decomposition catalogs.
We use this large sample to present one of the first comprehensive studies of the variation of galaxy radius with the environment – a relationship that has remained enigmatic with over a decade of conflicting results. With >5𝝈 confidence, we confirm that galaxies in denser environments are ~10-20% larger than equally massive counterparts in less dense regions of the Universe. We verify the presence of the above correlation separately for disk-dominated, bulge-dominated, star-forming, and quiescent sub-populations. We posit that the above correlation could be driven by assembly bias in dark matter halos and the varying prevalence of galaxy mergers in different environments.
42. জ্যোতির্পদার্থবিদ্যা বিভাগ আয়োজিত সাপ্তাহিক আলোচনা
বক্তাঃ অধ্যাপক বিমান নাথ, রামন গবেষণা কেন্দ্র, বেঙ্গালুরু
বিষয়ঃ গ্যালাক্সির অশনি সংকেত
সময় ও স্থানঃ ৩০ নভেম্বর, দুপুর ২টো ৩০ মি, এ. কে. বসাক প্রেক্ষাগৃহ
সারাংশঃ
বিজ্ঞানীরা লক্ষ করেছেন, যে সব গ্যালাক্সিতে নক্ষত্র জন্মের হার খুব বেশি, সেগুলোতে উত্তপ্ত গ্যাসের হুটোপাটিতে এমন অবস্থা তৈরি হয় যে, সেই গ্যাস তুমুল বেগে গ্যালাক্সির বাইরে গিয়ে ছিটকে পড়ে। এই সব গ্যালাক্সিতে তখন ঝড় ওঠে। বিজ্ঞানীরা সেই ঝড়ের সংকেত পেয়েছেন বিভিন্ন পর্যবেক্ষণে। সাম্প্রতিক গবেষণায় জানা গেছে যে এই ধরনের ঝড় কোনও গ্যালাক্সির ক্রমবিকাশের ক্ষেত্রে খুবই তাৎপর্যপূর্ণ। অর্থাৎ, গ্যালাক্সির ইতিহাস বুঝতে গেলে এই ঝড়ের খুঁটিনাটি জানা জরুরি। শুধু কি গ্যাসের তাপমাত্রা বেশি হলেই ঝড় ওঠে, না কি নাক্ষত্রিক আলোর চাপেও কিছু গ্যাস বেরিয়ে আসতে পারে? এই ঘটনায় নভোরশ্মির (কসমিক রে) ভূমিকা কী? অথবা ধুলোবালির? প্রাচীন গ্যালাক্সিতেও কি এই রকম ঝড় উঠত? এই বিষয়ে আমার কিছু গবেষণার কথা জানাবো এই আলোচনায়।
41. Colloquium at the School of Astrophysics
Speaker: Prof. Somnath Bhardwaj, IIT Kharagpur.
Title: Cosmology with the redshifted HI 21-cm line.
Date and Time: 22nd November, 2023, 2.30PM at P. C. Mahalanobis Auditorium.
Abstract:
The redshifted 21-cm line originating from the hyperfine transition in the ground state of neutral Hydrogen (HI) appears as a faint background at low frequencies. Observations of the spatial and angular fluctuations in this background radiation hold the potential of allowing us to study various aspects of the evolution of the Universe. This talk will discuss the predicted signal, and also present some efforts towards observing this with the GMRT.
40. Colloquium at the School of Astrophysics
Speaker: Dr. Manajit Sengupta, Chief Scientist in Predictive Analytics and Sensing, National Renewable Energy Laboratory (NREL), USA.
Title: Understanding Clouds and Radiation to Mitigate Climate Challenge.
Date and Time : 8th November, 2023, 3.30PM at P. C. Mahalanobis Auditorium.
Abstract:
Sunlight is free and it might just provide our way out from destructive climate change. Our goal is to understand the behavior of sunlight or solar radiation reaching the earth’s surface so that it can be optimally harnessed by energy generating systems. There are many questions we seek to answer but some of the most important ones are related to availability and variability of solar radiation all around the globe. This is a challenging task as the earth’s atmosphere interacts with solar radiation in complex ways. This means that solar radiation reaching the surface is highly variable due to interactions with clouds, aerosols, water vapor and atmospheric gases. We use ground-based measurements, satellite-based measurements, weather prediction models and climate models to measure, model and predict solar radiation. In this presentation, I will provide an overview of these methods, how they have advanced over the years, and what we plan to do to address outstanding challenges.
39. Colloquium at the School of Astrophysics
Speaker: Dr. Saumyadip Samui, Presidency University, Kolkata.
Title: First Stars and Cosmic Rays
Date and Time: 1st November, 2023, 3.30PM at Astrophysics Classroom
Abstract:
According to the Big Bang cosmology, the first stars were likely to form around redshift 30-20, known as the cosmic dawn. The direct detection of these stars is yet to be achieved, which is one of the goals of the JWST. Thus, indirect probes such as the 21cm signal from the cosmic dawn can provide insight into the nature of the first stars. In this talk, we will discuss some aspects of these first stars and how the 21cm signal can be used to probe them. In particular, high energy cosmic rays generated by the first stars would modify the global 21cm signal, and an accurately detected signal would reveal their physical properties.
AUTUMN BREAK
38. Colloquium at the School of Astrophysics
Speaker: Prof. Bhubanjyoti Bhattacharya, Lawrence Technological University, USA.
Title: Select Puzzles in Flavor Physics.
Date and Time: 11th October, 2023, 3.30PM at P. C. Mahalanobis Auditorium.
Abstract:
Precision B-physics experiments have revealed interesting deviations from Standard Model predictions. While new physics still eludes direct searches, flavor physics may provide some hints of new physics. I will present a few interesting puzzles from B-meson decays, resolutions of which may clearly identify a path for new physics discovery.
37. Colloquium at the School of Astrophysics
Speaker: Dr. Anupreeta More, Inter-University Centre for Astronomy and Astrophysics, Pune.
Title: Detection of Gravitational Wave Sources and Gravitational Lensing Effects
Date and Time : 4th October, 2023, 3.30PM at SoA Classroom.
Abstract:
Detection of gravitational wave sources consisting of massive binary black holes (BBH), in particular, is still a challenge due to contamination from noise transients called glitches. I will discuss our efforts to distinguish BBH from specific kinds of glitches. Gravitational lensing of gravitational waves is expected to be detected in the near future. I will present an improved statistic which will help identify candidate lensed GW events. The stellar population located within lensing galaxies are thought to produce distortions in the gravitational wave signals referred to as microlensing. I will also discuss how severe such microlensing effects are going to be and how they may affect detection of strongly lensed GW events.
36. Colloquium at the School of Astrophysics
Speaker: Prof. Dhruba Gupta, Department of Physical Sciences, Bose Institute, Kolkata.
Title: The Cosmological Lithium Problem in Nuclear Astrophysics
Date and Time: 27th September, 2023, 3.30PM @ P. C. Mahalanobis Auditorium.
Abstract:
The cosmological lithium problem is one of the important unresolved problems in nuclear astrophysics at present. The Big Bang Nucleosynthesis (BBN) theory overestimates the observed abundance of 7Li by a factor of about three, while it is extremely successful in accounting for the observed abundance of the lighter elements. The BBN model relies on the experimentally determined nuclear reaction rates. Thus, the search for a nuclear physics solution to the Lithium anomaly requires accurate measurements of the reaction cross sections. In particular, the 7Be destruction reactions deserve attention because 7Be is the main source of primordial 7Li. I would talk about our experiment, measuring the destruction of 7Be with deuterons at the HIE-ISOLDE radioactive ion beam facility of CERN. The excitations in the (d,p) channel lead to an astrophysical S factor ~ 70% higher than that used in BBN calculations for three decades. However, this does not alleviate the primordial Li problem and it may require new physics to address the anomaly.
35. Colloquium at the School of Astrophysics
Speaker: Prof. Mala Das, High Energy Nuclear & Particle Physics Division, Saha Institute of Nuclear Physics, Kolkata.
Title: The Initiative of Dark Matter Direct Search at Jaduguda Underground Science Laboratory, India.
Date and Time: 20th September, 2023, 3.30PM @ A.K. Basak Auditorium.
Abstract:
Dark matter (DM) consists of about 27% of the mass energy budget of the Universe and the detection and exploration of the nature of DM is an important topic of research in Astroparticle Physics. Among the several candidates, the WIMPs (Weakly Interacting Massive Particles) are the most favourable candidates of DM. DM does not emit or reflect electromagnetic radiation and it can be inferred through the gravitational interaction only. Therefore it is very challenging to detect dark matter by the usual particle detection methods and the events are dominated by the backgrounds. Several experiments at different underground labs are going on worldwide to search for dark matter directly. In India, there is an initiative to carry out such experiments at the JUSL laboratory in recent years. The JUSL, Jaduguda Underground Science Laboratory, is situated at a depth of 555 meter underground at the Jaduguda mine at UCIL, India. The radiation backgrounds at JUSL, such as neutrons, gamma-rays, cosmic muons, radon etc have been measured and/or simulated and more advanced measurements are underway. The small scale detector for DM search has been fabricated at the laboratory with active superheated liquid and coupled to the acoustic sensor and DAQ system. The system ran at the underground lab for about 4 months at 5.8 keV thresholds for a few kg-days of exposure. In this talk, an introduction to the dark matter search and challenges of such experiments will be discussed. The first results from the run at JUSL on the upper limit on WIMP-nucleon cross section for low WIMP mass along with the projected sensitivity for the future larger mass detector will be presented.
34. Colloquium at the School of Astrophysics
Speaker: Prof. Pratik Majumdar, Saha Institute of Nuclear Physics, Kolkata.
Title: Multimessenger Astroparticle Physics Using Photons and Neutrinos.
Date and Time: 23rd August, 2023, 3.30PM @ P. C. Mahalanobis Auditorium
Abstract:
Understanding the sources of cosmic rays has been one of the outstanding problems in cosmic-ray physics since their discovery more than a hundred years ago. Only recently, with the advent of new generation telescopes and detectors, this field got a boost in understanding the origin of cosmic rays and the acceleration of particles in those enigmatic sources. It has become clear that it is not enough to only look at photons emitted from these sources in order to understand them, but a comprehensive understanding may be obtained by looking at other messengers, namely neutrinos and gravitational waves. In this talk, I will discuss the connection between neutrinos and photons in understanding the sources of cosmic rays and also outline the future directions in multimessenger astroparticle physics.
33. Colloquium at the School of Astrophysics
Speaker: Dr. Priyarshini Ghosh, NASA Goddard Space Flight Center.
Title: Overcoming Engineering Problems in a Zinc-Sulfide Plastic Scintillator and Introducing a Quantum Dot Gel-Based Scintillator.
Date and Time: 16th August, 2023, 3.30PM @ P. C. Mahalanobis Auditorium
Abstract:
Great detectors are born from great engineering, but I’d like to present to you an underdog and a newcomer scintillator. The underdog is ZnS, which was the first ever material to be used as a scintillator, but has since been relegated to use in thin films with low fast-neutron detection efficiency due to its opacity to its own fluorescence despite having a high light yield. The Micro-Layered Fast-Neutron Detector (MLFD) has been designed by way of geometric orientation to overcome this light opacity, and thereby boast a higher fast neutron detection efficiency. It is also inherently discriminant to gamma rays, thus not requiring pulse-shape discrimination (PSD) in environments containing both fast neutrons and gamma rays, where neutron detection is required exclusively. Originally built for accident-tolerance testing of nuclear reactor fuels, the MLFD can also be used in Special Nuclear Materials searches. The second detector, Scintillation Hydro-Gel for Isotopic Neutron Emitters (SHINE), introduces a newcomer to the field of scintillation: environmentally-friendly quantum dots (QD) in a gel-based shapeshifter matrix. The gel format incorporates benefits of both solid and liquid scintillators while avoiding their respective disadvantages, such as continuous filtering of contaminates, slow throughput of containers, and higher base component costs in liquid scintillators, and ‘dead’ voids associated in solid scintillators. SHINE uses InP/ZnS, an eco-friendly QD with a large Stokes shift to prevent self-absorption of light for thermal neutron detection. SHINE has been successfully tested and demonstrates promise as a replacement for current 3He neutron detectors, and has potential use in hand-held, compact neutron detection units.
32. Colloquium at the School of Astrophysics
Speaker: Dr. Sibasish Laha, NASA Goddard Space Flight Center.
Title: The Fascinating Stories of Supermassive Black Holes at the Centers of Active Galaxies.
Date, and Time: 9th August, 2023, 3.30PM @ P. C. Mahalanobis Auditorium
Abstract:
A black hole is a striking example of a prediction of Einstein's general relativity. Although it took many decades before the physical concept of a black hole was fully understood and widely accepted, recent years have seen rapid advances on both the observational and theoretical side. The physics of black holes and matter surrounding the black holes are still an enigma. For example, we still do not clearly understand how matter falls in from large distances into the accretion disk. The accretion disk is an important component of the central engine of the bright Active Galaxies (AGN), the luminosity of which outshine even the host galaxy stellar emission. We also do not understand how exactly a jet is launched, nor do we understand how the winds emitted from the accretion disk interact with the host galaxy. Today I will talk about some of the most recent fascinating discoveries made in supermassive black holes (mass >10^6 solar mass) using NASA missions.
31. Colloquium at the School of Astrophysics
Speaker: Prof. Subhadeep De, IUCAA
Title: Quantum Clock for Exploring Fundamental Science
Date and Time: 2nd August, 2023, 3.30PM, P. C. Mahalanobis Auditorium
Abstract:
Atomic clocks having unprecedented accuracy are realized either by probing forbidden optical transitions of: neutral atoms localized in an optical lattice or a single atomic ion trapped in an electrodynamic trap. The tick rate of such clocks is influenced by unimaginably tiny perturbations of the energy states associated with clock transitions of the atoms. The resulting change in tick rates of the clocks could even be caused by variations of the fundamental constants, breaking of fundamental symmetries, gravitational red-shifts at millimeter scale, gravitational waves, cosmic microwave background, and so on. Thus, the intercomparison of the geographically distributed ultra-stable and highly accurate optical atomic clocks (quantum clocks) acts like “networked quantum sensors” and are used to explore the foundations of science, geodetic measurements, and testing the general theory of relativity. At the Precision & Quantum Measurement laboratory (PQM-lab: https://pqmlab.iucaa.in/), IUCAA we are developing an optical atomic clock based on trapped ytterbium-ions and aiming to explore fundamental aspects of science using it. I shall discuss some of these in my lecture.
SEMESTER BREAK
30. Colloquium at the School of Astrophysics
Speaker: Prof. M. Sivakumar, Hyderabad Central University, Chief Coordinator, Physics Training and Talent Search
Title: Higher Education in Physics: Problems and Prospects
Date and Time: 12th April, 2023, 2.30PM, P C Mahalanobis Auditorium
Abstract:
The talk starts with issues confronting physics education at UG/PG level and discusses a new program "Physics Training and Talent Search" for students and teachers, which attempts to address some of these issues. I will trace the core values, training methodology and details of the program, emphasising the novelty at each stage. I will conclude with further scope and limitations.
29. Colloquium at the School of Astrophysics
Speaker: Prof. Debasish Majumdar, Theory Division, SINP
Title: A Humble Account of Multifaceted Dark Matter
Date and Time: 5th April, 2023, 3.45PM, AK Basak Lecture Theatre
Abstract:
Dark Matter in the Universe is still an enigma. These huge amount of unknown and unseen mass, accounting for more than 80% of the total masss content of the Universe can only be percieved by it's gravitational influence. It plays important role in the structure formation with the network of Galaxies and clusters. In the absence of direct evidence of this enigmatic matter, the other possible indirect evidences of dark matter are vigorously pursued while new endeavours are being made for direct evidence. It may so happen that dark matter is not just a one-component entity but of various types with a mass range that may extend from eV scale to TeV scale. It may be of
different kinds depending on their cosmic history as also on their particle nature. There are attempts to understand the particle nature of dark matter with theories beyond standard model of particle physics. More recently the interacting dark matter scenario gained a lot of interest whereby the influence of self interacting dark matter is probed. This phenomenon can have influence on galactic dark matter halo and galactic processes. In addition, primaordial black hole as a dark matter candidate is also gaining interest. Thus dark matter physics encompasses three important major aspects of physics, namely astrophysics, cosmology and particle physics. In the presentation, these multifaceted nature of dark matter as envisaged by the researchers on this very interesting topic, will be discussed.
28. Colloquium at the School of Astrophysics
Speaker: Dr. Jayanta Dutta, Harish Chandra Research Institute
Title: Formation of the very FIRST STARS (primordial stars) in the Universe, and their survival possibility
Date and Time: 29th March, 2023, 3.30PM, Mathematics Lecture Theatre I
Abstract:
In this talk, we will briefly discuss the physical concept of the formation of the very first stars in our observable universe with a particular focus on their possible existence in the present-day galaxies. The entire complex process is reviewed from the point of view of a broad audience who are likely to gain a rudimentary understanding on this highly exciting area of "Theoretical Cosmology". Within that framework, we present a simple computational set-up of classical solid-body rotations for different realizations in terms of strength of rotational support that mimics the actual unstable gas-clumps formed within the dark matter minihalo in any cosmological simulation. The simulations are capable of investigating the protostellar evolution after the formation of the first protostar for highest rotating clumps (~20%) as compared to our previous studies. In this context, we also elaborate our current understanding of their probability of survival as main-sequence stars till today.
27. Colloquium at the School of Astrophysics
Speaker: Prof. Pijushpani Bhattacharjee, Syracuse University
Title: "Seeing" Supernova Neutrinos in Dark Matter Detectors
Date and Time: 22nd March, 2023, 3.30PM, PC Mahalanobis Auditorium
Abstract:
Stars shine by burning hydrogen into helium through nuclear fusion reactions in their cores. When a massive star (with mass typically more than eight times the mass of the sun) exhausts its hydrogen supply, the hydrogen burning ceases and energy production temporarily decreases. The resulting diminished radiation pressure is unable to support the star's core against its own gravitational pull, and the core begins to contract. This triggers a complex chain of events that eventually leads to the spectacular phenomenon of core-collapse supernova (CCSN) whereby the entire star explodes, leaving behind a compact remnant in the form of a neutron star or a black hole depending on the final mass of the core. In this process close to 99% of the gravitational binding energy (few times 10^{53} erg) of the stellar core is released in the form of neutrinos (and antineutrinos) of all flavors with energies up to a few tens of MeV over a timescale of about 10 seconds. Several large experimental facilities around the world are waiting trigger-ready to detect the neutrinos from the next nearby CCSN, after the historic first detection of neutrinos from the supernova SN1987A located in the Large Magellanic Cloud (LMC) at a distance of about 50 kpc from Earth. Since neutrinos are the only particles that travel essentially unimpeded from the stellar core to the detector, detection of supernova neutrinos can reveal extremely valuable information about not only the supernova process itself but also various aspects of fundamental physics of neutrinos themselves.
In this talk, after giving brief overviews of the CCSN mechanism, the basic physics of supernova neutrino detection and various currently operating and upcoming detectors, I shall discuss how some of the next-generation large detectors (specifically, liquid xenon based detectors) being planned for a different purpose, namely, dark matter detection, will also be able to detect the neutrinos from nearby (within about ten kiloparsec from earth) CCSN events. In addition, such detectors will have the potential to provide useful information about the distribution of the total SN explosion energy going into different neutrino flavors, which is in general not possible for other types of neutrino detectors.
26. Colloquium at the School of Astrophysics
Speaker: Dr. Ritesh Ghosh, NASA GSFC
Title: The curious case of Changing-Look Active Galactic Nuclei (CLAGNs)
Date and Time: March 15th 2023, 2.30 PM, A K Basak Auditorium
Abstract:
Active Galactic Nuclei (AGN) are one of the most energetic phenomena in the Universe. The central region (< 1pc) of these galaxies produces panchromatic emissions ranging from radio to Gamma rays through several physical processes. This emission arising from the tiny central region of an AGN (comparable to the size of the solar system) well surpasses the entire starlight emission from the whole galaxy. The origin of this emission has now been established to arise from the conversion of gravitational energy of the particles falling onto the supermassive black hole (>10^6 solar mass), the process known as accretion. Large amplitude variability timescales in AGN are of the order of 10^5 years and hence beyond the human lifetime. Though extremely rare, following recent wide-field optical surveys, there have been discoveries of such significant changes in AGN luminosity in a matter of months-years, thus pointing to rapid changes in accretion. This phenomenon, popularly known as changing-look AGN, has opened up new avenues to understanding the physics of accretion. In this work, I present one of the most interesting and enigmatic AGN, 1ES 1927+654, which has shown a 50 times optical/UV flux increase in ~3 months, and the X-ray flux vanishes and comes back after 200 days. A complete multi-wavelength view using radio, optical, UV, and X-ray telescopes suggests a magnetic flip of the black hole is responsible for this changing-look behavior.
25. Colloquium at the School of Astrophysics
Speaker: Dr. Ritoban Basu Thakur, NASA JPL and California Institute of Technology
Title: The earliest achievable glimpses of our universe: how quantum technology enables cosmological and astrophysical science.
Date and Time: March 1st 2023, 3.30 PM, A K Basak Auditorium
Abstract:
Precision Cosmology has been teaching us about the greatest mysteries of the origins of our universe and the formation of structure through cosmic epochs. This talk will review some of the biggest open questions facing modern physics addressed through observational cosmology. The talk will focus on how the instruments that perform these observations are actualized. Finally, some future-looking instrumentation efforts being developed at Caltech-JPL will be reviewed, and connections to other branches of physics will be made.
24. Colloquium at the School of Astrophysics
Speaker: Prof. Koushik Dutta, IISER Kolkata
Title: Some Implications of Early Matter-Dominated Epoch
Date and Time: Feb 22nd 2023, 3.30 PM, Mathematics Lecture Theater -I
Abstract:
Cosmic inflation at the very beginning of the Universe solves some of the most outstanding problems of the hot big-bang cosmology. In this case, inflation ends with an epoch of reheating that creates a radiation-dominated Universe. At the same time, the epoch of nucleosynthesis must have happened also in a radiation-dominated universe with a temperature of around MeV. But, the epoch between reheating and nucleosynthesis need not necessarily be radiation dominated, and any alternative expansion history of the universe does not violate any existing observations. In this talk, I will discuss some possible consequences of this intermediate epoch being dominated by a matter-like oscillating scalar field. In particular, in this scenario, I will talk about how CMB observables and dark matter abundance are related, and how possible primordial black hole productions are altered.
23. Colloquium at the School of Astrophysics
Speaker: Prof. Amitava Datta, University of Western Australia
Title: Application of deep learning in astrophysics
Date and Time:Feb 15th 2023, 3.30 PM, P C Mahalanobis Auditorium
Abstract:
The aim of this talk is to attract students to learn and use deep learning techniques for astrophysical data processing and classification. I will introduce fundamentals of deep learning, stochastic gradient descent and back propagation. I will discuss two of the simplest and widely used deep learning models, multi-layer perceptron (MLP) and convolutional neural networks (CNN), that have been used extensively in astrophysics recently. I will discuss how seemingly disparate problems like gravitational wave source localisation and searching for exoplanets have similar properties that are useful for applying deep learning techniques. The talk will be based on the two deep learning models mentioned above, including examples of research done by recent Presidency alumni. The talk will be at a preliminary level and no background in deep learning will be assumed.
22. Special Seminar at the School of Astrophysics
Speaker: Dr. Subhayan Roy Choudhury, Lawrence Berkeley National Laboratory
Title: ELECTRONIC EXCITED STATES : THE SYMBIOTIC FRIENDSHIP OF THEORY AND EXPERIMENT
Date and Time: 10th February, 2023, 11:00am, AK Basak Auditorium
Abstract:
Investigation of excited state properties is one of the most efficacious avenues for probing the electronic structure of materials. Evidently, dedicated theory-efforts are needed to complement the experimental research on this front. At the same time, leveraging the rapidly expanding database of experimental spectra, computational spectroscopy can offer valuable insights on the methods and approximations employed in electronic structure theory and thereby inspire the formulation of new theoretical approaches. Following a brief “teaser” report on X-ray absorption to demonstrate the role of simulations, in this talk I will explore the efficacy and interrelation of two popular first-principles approaches in the context of spectroscopy. I will show that, by constraining the population of desired subspaces, the excitation energies for low-lying states can be calculated easily. For de-excitation to the core-level I will compare two popular theoretical frameworks (the linear-response approach and the constrained-occupation approach) and comment on their limitations. I will demonstrate that an inexpensive determinant-based formalism reliant only on two self-consistent field calculations is typically sufficient for modeling such processes. Equipped with this understanding, we can develop a flexible framework for simulating the resonant scattering process by treating the effects of the core-excitations within the constrained-occupation approach and valence excitations with the linear-response method. Such a division of treatment not only ensures fast and accurate simulation of the spectrum, but also helps with its interpretation by automatically assigning the spectral features to the relevant electronic transitions.
21. Colloquium at the School of Astrophysics
Speaker: Prof. Parthasarathi Majumdar, IACS
Title: Must we quantize Gravity ?
Date and Time: 8th February, 2023, 3.30PM, PC Mahalanobis Auditorium
Abstract:
Beginning with Einstein's rationale for introducing the concept of photons through his Light Quantum Hypothesis, we enquire if issues,, similar in spirit, exist for Einstein's General Relativity. We cite two arguments in favour of a `yes' answer to this question, one dealing with spacetime singularities, and the other with black hole thermodynamics. We then classify the existing theoretical approaches to quantum gravity according to their scope and merits. Focusing on one approach known as Loop Quantum gravity, we outline its basic properties, and survey how it leads to a solution of one of the two conundra of GR discussed earlier. Time permitting, we shall briefly discuss some recent work which brings in Loop Quantum Gravity to recent direct detection of gravitational waves at observatories like LIGO, VIRGO and KAGRA, predicting a lower bound on the area of the remnant of all compact binary coalescences, irrespective of the astrophysical nature of the inspiralling components as well as the remnant. We mention how this, together with GW detection data, might lead to a constraint on neutron star equations of state, for binary neutron star mergers.
20. Colloquium at the School of Astrophysics
Speaker: Prof. Manik Banik, SNBNCBS
Title: Bell’s theorem: The Most Profound Discovery of Science
Date and Time: 1st February, 2023, 3.30PM, AK Basak Auditorium
Abstract:
Nobel Prize in Physics 2022 is awarded to Prof. Alain Aspect, Prof. John F. Clauser, and Prof. Anton Zeilinger for the experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science. Their works are fundamentally based on a seminal theorem derived by John Stewart Bell in 1964. What does Bell’s theorem tell us? Why should we learn this theorem? While Henry P. Stapp, an American mathematical physicist, describes Bell’s theorem as the most profound discovery of science, to Prof. Aspect it is a naive view of an Experimentalist. In my presentation, I will first discuss the historical and philosophical background of Bell’s 1964 theorem. I will then explain which classical world views are challenged by this theorem and why the experiments of Aspect-Clauser-Zeilinger are worthy of the Nobel prize. Finally, I will briefly discuss how this basic theorem of quantum foundations motivates the new era of 2nd quantum revolution.
19. Colloquium at the School of Astrophysics
Speaker: Prof. Indranil Chattopadhyay, ARIES
Title: Effect of composition in determining the solution of matter flow in relativistic astrophysics
Date and Time: 18th January, 2023, 3.30PM, PC Mahalanobis Auditorium
Abstract:
Black holes cannot be observed directly, it's presence has to be inferred from matter behaviour around it. Matter falling into it is heated to temperatures up to or more than tens of billion degree Kelvin. At such temperatures the matter is in plasma state while also obey equations of motion of a fluid. The physics of such matter is understood by analysing the radiation emitted by these plasma. However, the composition of accreting matter is not known at all, although composition should crucially affect the spectrum and the brightness of the object. We use a relativistic equation of state which depends on the composition of the flow and we show that composition indeed controls the accretion solutions qualitatively as well as quantitatively. We also show that the relativistic jets launched from these accretion discs also depend on composition of the plasma. To the extent that while an accretion disc which is composed of pair plasma fluid do not form shocks, an electron positron jet on the other hand produces so many structure that it tends to disrupt. Numerical simulations of jets also show that by varying the composition but same injection parameters, one can produce jets with vastly diverse morphology and propagation speed. Such detailed plasma behaviour in strong gravity has a very interesting impact on observations.
18. Colloquium at the School of Astrophysics
Speaker: Dr. Mukul Bhattacharya, Penn State University
Title: Magnetised outflows as potential sites of heavy element nucleosynthesis and high-energy neutrinos
Date and Time: 11th January, 2023, 3.30PM, PC Mahalanobis Auditorium
Abstract:
While nuclei lighter than iron are fused over the course of typical stellar evolution, almost half of the elements heavier than iron are created through the rapid neutron capture process (r-process). These nuclei are thought to be produced in magnetised outflows from neutron-rich explosive events including compact mergers and core-collapse supernovae. In this talk, I will discuss the potential of neutrino-driven winds from strongly magnetised and rapidly rotating protomagnetars as plausible sites for r-process nucleosynthesis. The low entropy and fast expansion timescale in magnetised outflows facilitates the formation of heavy nuclei in comparison to thermal winds. As heavy nuclei can eventually produce ultra-high energy cosmic rays, we examine the acceleration and survival conditions for these nuclei. We also explore the propagation of these jets through a broad range of progenitors: from Wolf-Rayet stars which have shed their envelopes to supergiants which have not. In particular, we compute the time-dependent jet magnetisation and luminosity to analyse the criteria for a successful jet breakout, maximum energy deposited into the cocoon and also the structural stability of these magnetised jets. We show that high-energy neutrinos can be produced for extended progenitors especially blue and red supergiants, and estimate the detectability of these neutrinos with IceCube-Gen2.
SEMESTER BREAK
17. Special Colloquium at the School of Astrophysics
Speaker: Prof. Arka Banerjee, IISER Pune
Title: Cosmology with nonlinear structure formation: Simulations and Statistics
Date and Time: 16th December, 2022, 2PM, AK Basak Auditorium
Abstract:
The formation, evolution, and clustering of structures in the Universe, such as galaxies, is a sensitive tool to probe some of the deepest questions in physics: the properties of Dark Energy and Dark Matter, the total mass and hierarchy of the Standard Model neutrinos, among many others. On large scales, perturbation theory approaches have been successfully applied to extract almost all the information from structure formation. On smaller scales, there is a vast amount of untapped information, but perturbation theory approaches break down due to nonlinearities driven by gravitational collapse. Harnessing this small scale information will be the next big challenge in observational cosmology. I will discuss how structure formation on small scales can be accurately modeled through numerical simulations. I will briefly describe how the application of new numerical techniques are allowing us to model the nonlinear predictions of an ever-expanding set of theoretical models, such as cosmologies with massive neutrinos, Dark Matter with additional interactions, and so on. I will then focus on statistical measures to characterize the clustering of structures on small scales. The widely used 2-point correlation function fails to capture all the details of the nonlinear clustering, motivating the exploration of other summary statistics. I will discuss in detail one such set of summary statistics - the k-nearest neighbor distributions, which are easy to compute on a given dataset while being sensitive to clustering at all orders in N-point functions. The use of these summary statistics can tighten constraints on cosmological parameters of interest by up to a factor of 3 - equivalent to increasing the volumes of current cosmological surveys by a factor of 9.
16. Colloquium at the School of Astrophysics
Speaker: Dr. Partha Nandi , SNBNCBS,
Title: The Kink of the Gravitational Waves in a Oscillator Detector: An Emergent Geometrical Phase shift.
Date and Time: November 9th, 3.30 PM, AK Basak Auditorium
Abstract:
The detection of low frequency gravitational waves (GWs) astronomy has marked an advent of a new era in the domain of astrophysics and general relativity. Using the framework of interaction between GWs and a point particle-like detector, within a linearized gravity approach, we build a toy model which has potential to detect such low-frequency GWs. The detector is in simultaneous interaction with GWs and an external time-dependent (tunable) two-dimensional harmonic potential. We discover that in adiabatic approximation, low frequency gravitational waves interaction can lead to a quantal geometric phase in the quantum states of the detector which can be controlled by tuning the frequency of the external harmonic potential trap. We argue that such geometric phase detection may serve as a manifestation of the footprint of GWs. More importantly, our theoretical model may be capable of providing a layout to build a future detector for the detection of very small frequency (≤ 5 Hz) GWs.
15. Colloquium at the School of Astrophysics
Speaker: Dr. Sanskriti Das , Stanford University,
Title: Surprises from the X-ray observations of the hot circumgalactic medium
Date and Time: November 2nd, 3.30 PM, Meghnad Saha Auditorium
Abstract:
Despite being challenging to detect, the ≥106 K hot circumgalactic medium (CGM) is a treasure trove of galaxy evolution. By probing the hot CGM of the Milky Way (MW) using X-ray absorption lines, we have discovered a super-virial 107 K phase coexisting with the well-known virialized 106 K phase, featuring non-solar abundance ratios of light elements, α-enhancement, and non-thermal line broadening. I have also detected this super-virial phase of MW CGM in X-ray emission analyses. Detection of these surprising properties of the CGM along multiple directions in the sky suggests a strong connection between the hot CGM and past Galactic outflow(s). Observations of MW-like galaxies complement our observations of the Milky Way. We have discovered the hot CGM emission of an MW-mass galaxy NGC 3221 that is extended (≥150 kpc) and is massive enough to account for its missing baryons. The CGM is not isothermal, with the CGM within 100 kpc of NGC 3221 being super-virial, and fainter along the minor axis than the global average. These results, at par with our findings in the Milky Way, compel us to rethink the impact of galactic feedback on the hot CGM of star-forming galaxies without an active nucleus.
14. Colloquium at the School of Astrophysics
Speaker: Dr. Rukaiya Khatoon , North West University, South Africa
Title: Understanding Blazars through Temporal and Spectral properties
Date and Time: October 19th, 3.30 PM, P C Mahalanobis Auditorium
Abstract:
Blazars are characterized by significant flux variability across the entire electro-magnetic spectrum. The cause of the variability is still not well understood. However, long term flux distribution studies of blazars can provide hints towards the causes of such variations. A lognormal flux distribution is often observed in long duration blazar light curves and is usually attributed to disk-jet coupling. However, minute scale variations in the flux suggest a compact emitting region inside the jet, probably disconnected from the disc and favors the variations to be produced in the jet itself. I will discuss how a linear Gaussian variation of the intrinsic particle acceleration time-scale can produce such log-normal variation. Moreover, spectral index distributions can provide confirming evidence for the origin of the variability. Another striking feature of blazar is that they show complex spectral variability. The Spectral Energy Distributions (SED) of blazars have a double hump structure, with the low energy component peaking in the IR - X-ray regime, and is well known to be caused by synchrotron emission from ultrarelativistic electrons. However, the origin of the high energy component peaking at MeV-TeV gamma-ray energies, is still unclear. I will discuss possible clues for the origin of the high-energy emission and the location of the emission region during the different flux states of blazars, through the timing and the broadband SED analysis
13. Colloquium at the School of Astrophysics
Speaker: Prof. Surhud More, IUCAA
Title: Cosmology and Astrophysics from the Subaru Hyper Suprime-Cam survey
Date and Time: 12th October, 3.30PM, PC Mahalanobis Auditorium
Abstract:
The growth of large scale structure in the Universe is a result of the competition between the effects of dark matter and dark energy. Current and upcoming large galaxy imaging surveys are aimed at mapping this growth of structure to learn about dark matter and dark energy. Gravitational lensing, the bending of light due to gravity, induces tiny distortions in the shapes of the observed galaxies. These tiny distortions can be used to reconstruct a tomographic map of the matter distribution. I will report on the cosmological constraints on the matter density parameter and the amplitude of density fluctuations from the Hyper Suprime-Cam Survey conducted from the Subaru telescope. Furthermore, I will also discuss how we use the weak lensing signal to learn about the galaxy dark matter connection as well as the dark matter halos of satellite galaxies. Finally, I will discuss the upcoming Legacy Survey of Space and Time using the Vera Rubin Observatory and how it will revolutionize the field in the coming decade.
AUTUMN BREAK
12. Colloquium at the School of Astrophysics
Speaker: Dr. Dhruba Dutta Chowdhury, Yale University
Title: Constraining Dark Matter with Gravitational Heating and Cooling Processes
Date and Time: September 28th 3.30 PM, P C Mahalanobis Auditorium
Abstract:
One of the biggest unsolved problems in astrophysics is the following - What is the nature of dark matter? While Cold Dark Matter (CDM) is the most popular dark matter model, weakly interacting massive particles (the most likely particle candidates for CDM) remain undetected. An intriguing alternative is Fuzzy Dark Matter (FDM), where dark matter particles are ultralight bosons. Unlike in CDM, FDM halos consist of a central solitonic core, surrounded by an envelope of order unity density fluctuations. The envelope density fluctuations also interact with the soliton, causing it to wobble and oscillate. Using novel, high-resolution numerical simulations of an FDM halo, corresponding to a particular boson mass, I will demonstrate that the gravitational potential fluctuations associated with the soliton's wobble, its oscillations, and the envelope density fluctuations dynamically heat nuclear objects (e.g., central star clusters and supermassive black holes) and galaxies. As a result, nuclear objects, initially located at rest at the soliton center, migrate outwards over time until the outward motion is counteracted by dynamical friction and an equilibrium is reached. Similarly, a galaxy undergoes significant size expansion and central density reduction over a Hubble time. Generalizing these results for other halo and boson masses and comparing them with observations (such as galaxy size-age relation, measured offsets of supermassive black holes and nuclear star clusters from the centers of their host galaxies) will be able to constrain the boson mass. After discussing FDM, I will also briefly present my work on the peculiar galaxy NGC 1052-DF2 and show what we can learn about its mass distribution from the dynamical friction-induced orbital decay of its globular clusters.
11.Special Colloquium at the School of Astrophysics
Speaker: Prof. Dipankar Banerjee, Director, ARIES
Title: Aditya L1: India’s own solar mission to study the variability of the Sun
Date and Time: 11.45 AM on September 26th, Physics Lecture Theater 3
Abstract:
The Aditya-L1 mission is India's first dedicated spacecraft mission to study the Sun. It will enable a comprehensive understanding of the dynamical processes of the Sun and address some of the outstanding problems in solar physics and heliophysics. In this presentation I will first provide an overview on the seven payloads which are going to be hosted in this observatory. The variability of our nearest star to the sun influences our near earth environment and our space climate. I will provide some insights on these areas.
10. Colloquium at the School of Astrophysics
Speaker: Prof. Tapas Baug, SNBNCBS
Title: Formation of massive stars: Observational signatures of newly evolved theories
Date and Time: September 21st 3.30 PM,P C Mahalanobis Auditorium
Abstract:
In spite of their vast importance in the evolution of their host galaxies, the formation and evolution of massive stars are not yet well understood. They influence the galactic evolution and replenish the interstellar medium by their strong stellar winds, outflows, expanding HII regions and supernova explosions. Energetic from massive stars may also initiate the second generation of star formation. In addition to several other theories, two theories have gained considerable observational evidence in the past few years. One of them is accretion through filaments, and another one is a collision between two nearby molecular clouds. We identified these two mechanisms in operation to form the massive stars in several Galactic star-forming regions. In this talk, I shall present a general overview of observational aspects of star formation inferred from our studies.
9.Colloquium at the School of Astrophysics
Speaker: Dr. Soumya Chakrabarti, SNBNCBS
Title: Late-time Cosmology with Variation of Fundamental Couplings
Date and Time: September 14th 3.30 PM, P C Mahalanobis Auditorium
Abstract:
We discuss a few possible extensions of standard gravity that can drive the present cosmic acceleration as well as accommodate a mild cosmic variation of one or more fundamental couplings of nature. Cosmological consistency is ensured based on parametrizations of kinematic quantities. Data analysis of molecular absorption lines from different spectrographs is considered a reference for the variations of fundamental couplings at different redshifts.
8. Colloquium at the School of Astrophysics
Speaker: Dr. Debanjan Bose, SNBNCBS
Title: Messengers of High Energy Universe : Cosmic Rays, Gamma-rays and Neutrinos
Date and Time: September 7th 3.30 PM, P C Mahalanobis Auditorium
Abstract:
Cosmic rays, gamma-rays and neutrinos bring us information about the relativistic Universe. They provide us glimpses of the extremely energetic phenomena which are still beyond the scope of the most powerful accelerators on earth. At high energies cosmic rays, gamma-rays & neutrinos are produced in the vicinity of super massive black holes, neutron stars and due to shock acceleration caused by supernovae. However cosmic rays, mostly protons, being charged particles are deflected in their path, therefore their source of origin is still unknown. Thus to study the high energy Universe we have to rely upon gamma-rays and neutrinos, being neutral they are not deflected in their path and since they escape from deep interiors of astrophysical sources they can provide answers to many fundamental questions. In this presentation apart from discussing acceleration mechanisms for these cosmic messengers I will also talk about detection techniques. Coming decades are very exciting for astroparticle physics with upcoming detectors such as CTA, IceCube-Gen2 etc. I will briefly discuss them as well.
7. Colloquium at the School of Astrophysics
Speaker: Dr. Achintya Pal, IAPT
Title: Voyager Mission and the voice of Indian Classical Music
Date and Time: August 31st 3.30 PM, AK Basak Auditorium
Abstract:
NASA launched Voyager 1 and 2 in 1977 to explore interstellar space extending its original mission to study outer planets. Apart from numerous instruments for scientific study, the spacecrafts carried a golden record containing pictures, sounds and music from different regions of the earth with the hope that in the event of the spaceship encountering a civilization in any distant stellar system, its intelligent beings would come to know about us. Many of us may not be aware that a piece of Indian classical music finds a proud place in the selection of 27 musical items from various parts of the world. It is a song rendered by Surashri Kesarbai Kerkar of Atrauli-Jaipur Gharana.
ভয়েজার মহাকাশ মিশন (১৯৭৭) ও তার ভারতীয় মার্গসঙ্গীত-সংযোগ
পৃথিবীর মানুষের মনে বহুদিন থেকে একটি প্রশ্ন জেগেছে যে সুদূরবিস্তৃত এই মহাবিশ্বে সে কি একা, না কোনখানে তাদের মত আর একটি প্রাণীজগৎ এবং তার সঙ্গে বুদ্ধিমান সত্তা বিরাজ করছে? আন্তঃনাক্ষত্রিক স্থান (interstellar space) অন্বেষণের উদ্দেশ্যে NASA ১৯৭৭ সালে দু’টি মনুষ্যবিহীন যান ভয়েজার ১ এবং ২ মহাকাশে উৎক্ষেপণ করে। বৈজ্ঞানিক বহুবিধ গবেষণা ছাড়াও এই মিশনের আর একটি উদ্দেশ্য ছিল – অত্যন্ত অসম্ভাব্য হলেও, কোন বুদ্ধিমান প্রাণীজগতের সন্ধান আদৌ পাওয়া যায় কিনা। এই উদ্দেশ্যে পৃথিবীর বিভিন্ন অংশের ছবি, ভাষা, শব্দ এবং সঙ্গীত সম্বলিত একটি স্বর্ণ-রেকর্ড মহাকাশযানের সাথে প্রেরণ করা হয় যাতে দূর নক্ষত্রলোকের কোন প্রাণী যদি তা দেখতে পায় তাহলে তার বিষয়বস্তুর পাঠোদ্ধার করে আমাদের সম্বন্ধে জানতে পারবে। এই ভয়েজার যানের গতিপথের কালানুক্রমিক ইতিহাসের সাথে সাথে আলোচনা করা হবে ঐ রেকর্ডের ছবি, ভাষা-শব্দ এবং বিশেষতঃ সঙ্গীতের সঙ্গে ভারতীয় সংযোগের – যা হয়তো অনেকেরই অজানা।
6. Colloquium at the School of Astrophysics
Speaker: Prof. Soumen Mondal, SNBNCBS
Title: Star-formation, Pre-main Sequence Stars and Very Low Mass stars to Brown Dwarfs: Physical Insights
Date and Time: August 24th 3.30 PM, P C Mahalanobis Auditorium
Abstract:
Galactic star-forming regions are the formation sites of young stars in Pre-Main Sequence (PMS) different stages, including massive O, B type stars in H II regions. Multi-wavelength studies on such regions help to understand the census of PMS stars, their formation process, and the interaction of expanding H II regions harbouring massive stars with its natal molecular clouds. PMS stars first came into the spotlight due to their photometric variable characteristics. Very Low Mass stars (VLMs) belong to the spectral type of M dwarfs and have the lowest masses of 0.08–0.6 M⊙ and effective temperatures of 2500–4000 K, which are dominating the stellar populations by number (more than 70%). Brown Dwarfs (BDs) are sub-stellar objects with a mass ranging from 13 MJ (MJ : Jupiter Mass) to 75 MJ for solar luminosity. Spectroscopic and variability studies of these kinds of objects provide important parameters of fundamental parameters and their circumstellar atmospheres. In this presentation, I would like to highlight some of our interesting results obtained from our multiwavelength observations using spectroscopic and photometric methods that help us to understand the physical insights.
5.Colloquium at the School of Astrophysics
Speaker: Prof. Ushasi Datta, SINP, Kolkata
Title: Nuclei around the drip-line and its impact on the cosmic events
Date and Time: August 17th 3.30 PM, P C Mahalanobis Auditorium
Abstract:
Even after 100 years of discovery of the atomic nucleus by Rutherford, limits of the existence of nuclei are still uncertain. This is due to lack of proper understanding of the nature of interactions that bind atomic nuclei. The atomic nucleus is a complex quantum many-body system but its simple behavior can be explained by a mean nuclear field, containing many ingredients of the nucleon-nucleon interactions. The characteristics of that are the shell gaps at magic numbers, explained by Mayer and Jensen.
The study of Nuclear Shell structure around the drip-line and validation of theoretical prediction with the data may provide important information on nucleon-nucleon interaction. We have
investigated the properties of neutron-rich nuclei using radioactive ion beam. Very clear evidences have been observed for the breakdown and merging of long cherished magic shell gaps at N=20, 28. The nuclei around the drip-line are short lived and naturally do not exist on the earth. But surprisingly, evanescent rare isotopes imprint their existence in supernovae and other stellar explosive scenarios (rp, r-process etc.).
To understand those processes and synthesis of those elements, one has to create those nuclei in the laboratory to explore specific-properties. Due to their fleeting existence, indirect measurements are often only possible access to the information which are valuable inputs to the model for star evaluation process. Neutron star, remnant of supernovae is the densest matter, observed in cosmos. To understand that state of matter, some valuable properties of proton-rich and neutron-rich nuclei are key
issues. I shall discuss our achievements related to above mentioned facts using RIB in worldwide scenario.
4.School of Astrophysics Colloquium
Speaker: Dr. Namrata Roy, University of California at Santa Cruz.
Title: Star formation suppression and feedback in nearby passive galaxies
Time: 3:30-4:30 PM, August 10th 2022, P C Mahalanobis Auditorium
Abstract:
A key question in galaxy evolution is understanding how galaxies completely stop (or “quench”) their star formation towards the end of their lifetime. In spite of having the fuel necessary for forming stars, the lack of detected star formation in old massive galaxies indicates the presence of a feedback energy. Active galactic nuclei (AGN) driven feedback has been proposed to be the most efficient feedback mechanism capable of suppressing star formation - but direct evidence of such feedback in typical galaxies has been lacking. In this talk, I will present evidence from a series of papers that a new (and relatively common) class of early-type galaxies, known as ‘red geysers’, may represent AGN feedback in action. I will show that these low redshift galaxies, selected from SDSS IV - MaNGA survey, host low luminosity radio mode AGNs with signatures of large scale ionized gas outflows. I will present a multi-wavelength study of these red geyser populations from a variety of observational datasets and discuss their role in the global quenching of star formation. Finally, I will end by discussing the incredible amount of progress we will be able to make in detecting feedback and outflows from galaxies spanning a wide range of redshift using the James Webb Space Telescope
3. School of Astrophysics Colloquium
Speaker: Prof. Sunanda Banerjee, IACS.
Title: Fifty Years of Experimental High Energy Physics
Time: 3-4 PM, August 3rd 2022, P C Mahalanobis Auditorium
Abstract: The human mind has been trying to understand the fundamental constituents of matter almost from the beginning of human civilization. Through the work of great philosophers and then the Chemists and Physicists, the idea crystallized that all matters are built of quarks and leptons which interact among themselves through the exchange of vector bosons. The current understanding is expressed through the formulation of the Standard Model. In the last fifty years, a number of experimental findings paved the way of the Standard Model. Some of the key experiments will be elaborated in this talk. The experiments also showed that the Standard Model is not the last word and more thinking and experimentations are needed to reach the truth.
2. School of Astrophysics Colloquium
Speaker: Prof. Ritaban Chatterjee, PU
Title: Blazars in the Astrosat Era
Time: 3-4 PM, July 27th 2022, P C Mahalanobis Auditorium
Abstract:
1. School of Astrophysics Colloquium
Speaker: Dr. Shashwata Ganguly, University of Cologne
Title: Morphology, fragmentation, and dynamic balance: an investigation into early stages of structure formation in molecular clouds
Time: 3-4 PM, July 20th 2022, P C Mahalanobis Auditorium
Abstract:
How molecular clouds fragment and create the dense structures which go on to eventually form stars is an open question. In this talk, I will highlight various aspects of fragmentation and structure formation in young molecular clouds based on the SILCC-Zoom and SILCC deep-zoom simulations. The SILCC-Zoom simulations follow the self-consistent formation of molecular clouds in a few hundred parsec sized region of a stratified galactic disc, which include (self-) gravity, magnetic fields, supernova driven turbulence, as well as a non-equilibrium chemical network and treatment of the interstellar radiation field, with resolutions of ∼0.1 parsec. The SILCC deep-zoom simulations are an extension of the cloud scale SILCC-Zoom simulations and allow us to resolve structures with a maximum resolution of 0.0078 parsec (∼1600 AU). In my talk, I will focus on the interplay of different dynamical components (gravity, turbulence, magnetic fields etc.) that lead to the formation of dense, potentially star-forming structures at parsec and sub-parsec scales. I will further trace the morphology of forming sub-structures at various length scales, and attempt to connect it to their energetics. By tracing the time evolution of both the energetics and morphology, I will outline a possible scenario of how dense structures, and eventually stars emerge from the diffuse interstellar medium.
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