AR_final file_2018-19

Very massive stars at the end of their lives would undergo core collapse to generate a Black Hole. This is usually accompanied by a most spectacular explosion, known as a Gamma Ray Burst (GRB). Extensive research is going on at IUCAA on the study of black holes and the matter around them. At the centre of this activity is the Indian X-ray/UV astronomy satellite AstroSat. IUCAA, in collaboration with ISRO, operates the Science Support Cell for this mission, and interacts with a wide cross section of researchers across India, especially from the university sector. BLACK HOLES Over 50 birth events of black holes, namely GRBs, have been detected by the AstroSat team at IUCAA during the year. Several stellar mass black holes that are accreting material from a normal stellar companion have been studied extensively with AstroSat. In one such system, 4U1630-47, these observations have revealed that the black hole is spinning extremely rapidly, near the maximum allowed limit. In another system, Cygnus X-1, detailed modelling of intensity fluctuations has led to the conclusion that inward-propagating temperature fluctuations in the ``accretion disk'' created by matter falling into the black hole explains the observed variability pattern. Many supermassive black holes, millions of times heavier than the sun and residing at the centres of galaxies, have also been studied. Simultaneous multi-wavelength observations of the blazer 1H0323+342, an object of this class, have shown how, from time to time, material from the accretion disk is ejected at high speed forming jet-like outflow along the spin axis of the black hole. A more detailed description of the above, and of many other results from IUCAA’s research activities this year, may be found in the section “Research at IUCAA” later in this report. ( 41 )