India’s space observatory AstroSat has revealed new insights into the enigmatic behavior of a distant black hole, GRS 1915+105, demonstrating how it flickers in X-rays with exceptional accuracy. Located 28,000 light-years away within our Milky Way galaxy, this black hole system is assisting scientists in deciphering the extreme conditions surrounding one of the universe’s most formidable objects. Since its launch in 2015, AstroSat — India’s inaugural dedicated multi-wavelength space telescope — has been persistently observing GRS 1915+105. A group of Indian researchers from ISRO, IIT Guwahati, and the University of Haifa utilized two of its onboard instruments, the Large Area X-ray Proportional Counter (LAXPC) and the Soft X-ray Telescope (SXT), to analyze the black hole’s enigmatic signal pattern. They identified a recurring sequence: several hundred seconds of faint X-ray light, succeeded by a comparable duration of intense light. During the brighter intervals, they made a remarkable discovery — rapid X-ray flickers occurring 70 times per second, referred to as Quasi-periodic Oscillations (QPOs). These flickers ceased during the dimmer intervals.
The team traced this swift flickering to the corona, a superheated plasma cloud enveloping the black hole. In the bright phases, the corona shrinks and heats up, producing strong QPOs. In the dim phases, it cools and expands, leading to the disappearance of the flickers. The black hole is part of a binary system, drawing matter from a companion star into a hot, spinning disc. As this matter heats, it emits X-rays — the signals that AstroSat captures. This research, published in the Monthly Notices of the Royal Astronomical Society, offers scientists a more profound understanding of black hole environments. The results highlight India’s advancing capabilities in space-based astronomy and the significant role of AstroSat as a cosmic observatory.
