About Me:
Indu Kalpa Dihingia, Postdoctoral Fellow, TDLI-SJTU, Shanghai, China
Hello, welcome to my webpage. There is an ample number of questions in my mind about the universe, how it came to existence? How exactly is it working? etc. etc. People from different front are trying to find some answers to all those questioned. For me, right now trying to understand the accretion flow around black holes and naked singularity. Please visit my research section for more details.
I was born and raised in Dhemaji, Assam, India. I completed a Bachelor of Science in Physics (2007-2012) from DHSK College Dibrugarh, under Dibrugarh University. I obtained a Master of Science in Physics (2012-2014) and obtained a doctorate degree in Physics (2020, supervisor Prof. Santabrata Das) from the Department of Physics of the IIT Guwahati, India.
Soon after my Ph.D. thesis submission, I moved as a postdoctoral Fellow to the IIT Indore in the discipline of astronomy astrophysics and space engineering (DAASE). I worked there from 2020-2022.
Currently, I am working as international overseas talent programme at Shanghai Jiao Tong University - Tung Dao Lee Institute, TDLI prize postdoctoral Fellow from 2022.
Current research:
Understand polarised emission from AGNs.
Finding evidences of low-angular momentum flow around compact objects
Semi-analytical model development around black holes.
X-ray polarisation modeling for BH-XRBs
Physics beyond Kerr black holes study higher order ring
Overview of my Ph.D. thesis:
In my Ph.D., I wokred to provide a comprehensive study of accretion flow around the Kerr black hole, where many layers of modifications are suggested to encompass the theoretical models to explain the observed high-energy emission from the compact objects. The Ph.D. thesis starts with a physically motivated two-temperature accretion flow model over the traditional and simplified single-temperature model that allows authors to incorporate all the relevant radiative processes in the accretion flow. Due to the extreme curvature of the space-time around the black hole, the use of the general relativistic effects is unavoidable in studying the properties of the accretion flow. Because of this, the authors study general-relativistic accretion flow around Kerr black hole and indicate the importance of the relativistic equation of state while studying accretion around Kerr black hole. We further extend the study of the relativistic accretion disc around Kerr black hole considering viscosity and shock-waves. We use their relativistic accretion flow model to explain the quasi-periodic oscillations (QPOs) and the hard X-ray emission in black holes. Moreover, they propose a possible physical mechanism to explain the origin of the high-frequency QPOs, and following this proposed mechanism, and they estimate the spin values of the black holes. In a way, the model formalism proposed in this thesis is potentially promising to account for the various observational quantities, namely QPOs, luminosity, black hole spin, etc.
In accretion physics, astrophysicist often adopts Newtonian hydrodynamics because of its simplicity. In Newtonian hydrodynamics, the pseudo-potential is commonly used to mimic the general relativistic effect around the black hole. For Schwarzschild black hole, Paczynsky and Wiita potential are being successfully used since 1980. The quest for such a pseudo-potential around Kerr black hole started from the 1980s; however, all the successes appear with great limitations. In this thesis, we could derive an effective potential around the Kerr black hole, which works seamlessly in all the range of black hole parameters without suffering any limitations. The thesis also showed that the Newtonian or non-relativistic limit of the hydrodynamics fails to provide a satisfactory description of the accretion flow around rotating black holes. Moreover, they propose a semi-relativistic approach that yields the dynamics of accretion flow very similar to the general relativistic approach with an acceptable range of accuracy.
Finally, we develop a two-temperature, semi-relativistic, magnetize accretion flow model around Kerr black hole. For the first time in literature, they were successful to self-consistently calculate the spectral energy distribution of an accretion flow around the Kerr black hole. we show that their model is viable to explain the observed spectral state transitions in low-mass X-ray binaries (LMXRBs).
Post Ph.D. research:
Magnetic fields are ubiquitous in astrophysical environments and play a vital role in driving accretion flow around the black hole. With the increase of the sophistication of astrophysical observations, developing a unified numerical model for accretion flow is essential. General relativistic magneto-hydrodynamical (GRMHD) simulations have been instrumental for modeling accretion flow around the black hole. Currently, I am working on GRMHD simulation using a code called BHAC. Our goal is to understand the launching mechanism of Astrophysical jets and disc-winds. Astrophysical jets and disc-winds are typically observed in BH-XRBs and AGNs. However, many physical details of jet launching and the driving of disc winds from the underlying accretion disc are still not fully understood. Our study finds, astrophysical jets launched due to Blandford & Znajek (BZ) mechanism and the disc-wind driven by the Blandford & Payne (BP) mechanism. Our models provide a possible template to understand spectral state transition phenomena in BH-XRBs.-