2026

Abstract: The 21-cm signal is a powerful probe of the high-redshift universe, offering a unique window into the cosmic dawn and the dark ages. In this talk, I will introduce the fundamentals of 21-cm cosmology and highlight its advantages in studying the early universe. Through specific examples, I will illustrate how the 21-cm signal can be used to constrain the nature of dark matter, provide independent confirmation of an excess radio background, and make predictions for galaxy surveys. Finally, I will present ECHO21, a new Python package designed to efficiently generate a large suite of models spanning the dark ages and cosmic dawn.

Abstract: Primordial features are scale-dependent departures from the leading order scale-invariant spectra of the primordial density perturbations produced by Inflation. Such unique traces contain a high degree of informativity and their detection can be used to identify non-standard inflationary trajectories. 

In this talk, I discuss recent advances in comparing feature models to cosmological data, focusing on Cosmic Microwave Background (CMB) anisotropies, and present primordial feature signals that provide interesting fits to anomalies in the data. While the models remain statistically indistinguishable from the standard slow-roll scenario, future measurements of the polarization of the CMB offer optimistic prospects for detecting such best fit candidates and shed light on their primordial origin.

Abstract: The sharpest images ever made (in the sense of angular resolution) are all at radio wavelengths --- most famously the black hole shadows reconstructed from the Event Horizon Telescope. Can comparable angular resolution be achieved at optical wavelengths? This talk will draw attention to several recent research groups who are attempting just that.   The key is to exploit a quantum-optical phenomenon known as the Hanbury Brown & Twiss (HBT) effect.   Most of the targets are stars, but there are more exotic things to image too...

Abstract: Primordial black holes (PBHs) serve as key probes of the early Universe and cosmic evolution. In this study, we explore the formation of PBHs near the QCD phase transition, driven by a broadly peaked inflationary scalar power spectrum. This mechanism naturally results in an extended PBH mass distribution and generates two distinct stochastic gravitational-wave backgrounds (SGWBs): a scalar-induced SGWB from second-order tensor perturbations at the time of PBH formation, and a merger-driven SGWB arising from the evolution of the PBH binary population. We analyze both SGWB components using Bayesian methods, incorporating data from the NANOGrav 15-year dataset and the first three observing runs of LVK. We also project the continuous-wave signals expected from mini extreme–mass-ratio inspirals (mini-EMRIs), enabling direct comparison with existing constraints from NANOGrav and LVK.

Our parameter-space analysis reveals regions where the combined SGWB signal may be detectable by future ground- and space-based gravitational-wave observatories. Notably, the extended PBH mass spectrum naturally leads to the formation of mini-EMRIs, which are promising targets for next-generation ground-based detectors such as upgraded versions of LVK, ET, and CE. In much of the parameter space, the astrophysical SGWB masks the primordial contribution in the frequency range accessible to ground-based detectors. As a result, in scenarios with extended PBH mass functions, the detection of mini-EMRIs provides a more reliable probe of the PBH landscape than SGWB measurements alone.

Abstract: The Event Horizon Telescope (EHT) has imaged supermassive black holes (SMBHs) at the centres of two galaxies, M87* and Sgr A*, and resolved the jet bases in a few additional SMBHs. Ongoing ground- and space-based upgrades to the EHT are expected to significantly advance our understanding of black hole accretion and jet physics. We are developing ETHER (Event Horizon and Environs), a curated and expanding database of nearby single and binary black holes for EHT and next-generation EHT (ngEHT) studies. Originally developed for target selection, ETHER extends the transformative science enabled by M87* and Sgr A* to a much broader population of SMBHs, bridging the gap between these two extremes. This unprecedented demographic survey advances studies of accretion and jet launching, provides new tests of general relativity, enables measurements of black hole masses and spins in dozens of SMBHs and potentially resolves gravitationally lensed rings in a handful of them. It also opens the possibility of resolving binary SMBHs and tracking their orbital decay during the gravitational-wave-emitting phase. In this talk, after briefly touching upon recent EHT results, I will present the status of ETHER and its “gold” samples of single and binary black holes for present and future EHT imaging of shadows, rings, and accretion inflows, and discuss modeling results for jet bases. I will also review expectations of observing these gold targets with the EHT and its upgrades, assess the capabilities and limitations of the current EHT, and evaluate the feasibility of near-future ngEHT observations.

Abstract: In the LCDM model, the formation and evolution of galaxies are inextricably linked to their surrounding dark matter haloes. However, baryonic processes within galaxies can in turn affect the dark matter distribution, notably through different feedback processes driven by stellar evolution and active galactic nuclei. I will review observational and theoretical tensions pertaining to the interplay between galaxies and their dark matter haloes, with the goal to leverage these challenges to either refine our understanding of baryonic processes within LCDM or guide the exploration of alternative models. On one side, observations concurrently reveal strikingly tight correlations between baryonic and dark matter masses, yet show a diversity in observed rotation curves at any given mass. On the other side, state-of-the-art cosmological simulations do not agree on the effect of feedback processes on dark matter haloes and are thus unable to reproduce the full spectrum of the observed diversity. Observational constraints on the evolution of the dark matter distribution and the scaling relations between baryonic and dark matter masses across cosmic time would help address these challenges, for example with the upcoming Square Kilometer Array. 

Abstract: Protoclusters are dense regions of molecular gas that represent the earliest stages of stellar cluster formation and the birthplaces of massive stars. Understanding the physical processes that govern their evolution is therefore essential for building a complete picture of massive star formation. In this talk, I will present results from two recent ALMA-based studies that investigate the roles of turbulence, magnetic fields, and gravity in massive protocluster environments. First, I will discuss our analysis of the G327.29 protocluster, where dust polarization observations are compared with the Velocity Gradient Technique (VGT), which is based on the modern theory of magnetohydrodynamic turbulence, to infer magnetic field morphology in dense star-forming regions. This comparison provides new insight into the complex physical conditions of protocluster environments, where turbulence, magnetic fields, and gravity jointly shape the gas dynamics. I will then present results from our other work, where we investigate the properties of turbulence in fifteen massive protoclusters from the ALMA-IMF survey using the C¹⁸O spectral line. By analyzing the kinematic structure and turbulent velocity statistics across these regions, we find that turbulence is supersonic in nature and maintained throughout the evolutionary stages of massive protoclusters, likely sustained by feedback from expanding H II regions. Together, these results offer a broader view of how turbulence, magnetic fields, and gravity influence the structure and evolution of massive star-forming regions.

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Abstract: Most massive stars conclude their lives in a violent core-collapse supernova (SN). A rare subset—superluminous supernovae (SLSNe)—exceed the luminosities of canonical core-collapse events by factors of 10–100. Although substantial progress has been made over the past decade in characterizing their observational properties, the physical mechanisms powering SLSNe and the nature of their progenitors remain open questions. In this seminar, I will provide a detailed overview of recent developments, including powering mechanisms such as magnetar spin-down, circumstellar interaction, and hybrid scenarios—emphasizing how each seeks to reproduce their extreme luminosities and diverse light-curve morphologies. I will discuss spectroscopic diagnostics that probe the composition and ionization of ejecta, with particular attention to emerging helium signatures in events traditionally regarded as hydrogen- and helium-poor. I will also examine the increasing number of SLSNe exhibiting light-curve undulations (“bumps”) and explore their potential origins in progenitor mass-loss histories, structured circumstellar media, or engine-driven variability. Recent observations of SN 2024ahr, SN 2024rmj, and SN 2024afav provide new constraints on helium abundance, ejecta–CSM geometry, and the late-stage evolution of massive stars. Together, these developments refine our understanding of SLSN progenitors and motivate future progress enabled by upcoming wide-field surveys such as the Vera Rubin Observatory’s LSST.

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