IUCAA Brochure 2024

High Energy Astronomy of Black Holes The enigmas of Black Holes are not easy to study due to the lack of any light information coming directly from them. However, black holes in X-ray binary systems and at the centres of active galaxies accrete material that results in copious amounts of radiation primarily in the X-ray and Ultraviolet bands. India's first multi- wavelength space observatory AstroSat has been vital and has allowed Indian astronomers to study the immediate environments near stellar mass black holes in X-ray binaries and super-massive black holes in active galaxies. IUCAA plays a major role in AstroSat, India's first dedicated multi-wavelength space observatory which has special instruments particularly sensitive to UV and different energies of X-rays. IUCAA researchers are members of instrument teams, run the Astrosat science support cell (ASSC), and host the payload operation centre for the CZTI instrument aboard the satellite. Some of the software for AstroSat was written by members of ASSC. The ASSC also runs training workshops, schools, and instrument calibration meetings which are extremely useful, enabling researchers all over India to use AstroSat, in writing proposals for scientific observations and analyzing its data. Using AstroSat, IUCAA researchers are also involved in studying complex processes in the innermost regions close to supermassive black holes (SMBH) in active galaxies (AGN) and stellar-mass black holes in X-ray binaries. They have found accretion disks that do not extend to the innermost stable orbit