The Department of Physics is organising a guest seminar on the topic “Observational Evidence for Black Holes in the Era of Mega-telescope and Multi-messenger Astronomy”. The seminar will be delivered by Dr Shubhrangshu Ghosh, Centre for Astrophysics, Gravitation and Cosmology (CAGC) & Department of Physics, SRM University Sikkim, on July 30, 2025.
Abstract
Black holes (BHs) are one of the most remarkable predictions of Einsteinian gravity. A plethora of overwhelming evidence appears to be quite compelling about the existence of astrophysical BHs in the observable Universe. These astrophysical BHs have, so far, been observed predominantly in two distinct mass flavors: as stellar-mass BHs in the range of ∼ (5 − 30) solar masses, ubiquitous and widespread in the galaxies, with several of them residing in close binary star systems; and as supermassive BHs (SMBHs) in the range of ∼ (10^6 − 10^10) solar mass dwelling in the nucleus/centre of virtually all large galaxies, and of yet unknown origin. Although invisible due to their event horizon, their presence is primarily inferred through accreting matter falling on them, ejection of powerful relativistic radio-emitting jets from their vicinity, often showing superluminal motion, orbital motion of stars around nuclei/centres of galaxies, and through detection of gravitational waves (GWs) from binary mergers. These BHs drive some of the most energetic phenomena in the observed Universe: with the stellar BH binary systems appearing as one of the brightest X-ray sources in our local galaxy, namely the BH X-ray binaries (BHXRBs) accompanied by strong X-ray variability in their spectrum; and on the other hand, the nucleus of active galaxies (AGNs) emit enormous amount of electromagnetic energy in all wavelengths, appearing as the most luminous persistent sources in the Universe. The measured masses of SMBHs are strongly correlated with properties of their host galaxies, suggesting that these BHs have a strong influence on the formation and evolution of entire galaxies, primarily through radio jet-AGN feedback, thus shaping much of our contemporary observed Universe. The recent direct imaging of SMBHs in the centre of Messier 87 and our galactic centre (Sgr A*) by Event Horizon Telescope (EHT) mission, and the first direct detection of GW in a coalescing binary BH system, GW150914, by the LIGO project, have provided a remarkable new window to this field. With the existing and upcoming next-generation telescope/detector facilities, both ground and space-based, like SKAO, ELT, Lynx, Athena, CTA, KAGRA, LISA, DESIGO, ET, including several Indian missions like AstroSat, XPoSat, INSIST, LIGO India, etc, which will provide a complete view of these high-energy sources through multi-messenger and multi-wavelength data with unprecedented accuracy.
Dr Ghosh will address these aspects, providing an overview of the field’s current status and future directions.
Join the session for an invigorating exploration through astrophysics!