A team of researchers from the Indian Institute of Technology Guwahati, in collaboration with U. R. Rao Satellite Centre (ISRO) and the University of Haifa in Israel, has decoded mysterious X-ray signals from a distant black hole located nearly 28,000 light-years away.
The black hole, named GRS 1915+105, was studied using data from India’s space observatory AstroSat. Researchers observed that its X-ray brightness alternated between bright and dim phases, each lasting several hundred seconds.
Black holes draw gas from the outer layers of their companion stars, producing extreme heat and releasing X-rays. By studying these signals, scientists aim to understand conditions in the regions near a black hole.
Professor Santabrata Das of the Department of Physics at IIT Guwahati said the team had identified new evidence of rapid X-ray flickering.
He said they found the first evidence of rapid X-ray flickering, repeating nearly 70 times per second (∼70 Hz), occurring during the high-brightness phases of the source. He explained that these fast flickers disappear during the low-brightness phases, a finding made possible by AstroSat’s observational capabilities.
According to the researchers, the X-ray brightness alternated between two distinct phases. During brighter phases, when the flickers were strongest, the corona around the black hole became more compact and significantly hotter. In contrast, during dimmer phases, it expanded and cooled, causing the flickers to disappear.
The observation suggests that the corona is not a fixed structure but changes shape and energy depending on the inflow of gas. The rapid flickering signals appeared only during the bright phases, showing a clear correlation between the compact, oscillating corona and the emission patterns.
The study provides insight into the extreme gravitational and thermal conditions near black holes and contributes to models of how they grow, release energy, and affect their surroundings. Researchers also suggest that such findings may improve understanding of how black holes influence the evolution of galaxies.
Dr Anuj Nandi of URSC, ISRO, highlighted the significance of the discovery.
He said the study provides direct evidence for the origin of X-ray flickering and that the flickering is linked to modulations in the corona surrounding the black hole.
The research has been published in the journal Monthly Notices of the Royal Astronomical Society. The paper was co-authored by Professor Santabrata Das and research scholar Seshadri Majumder of IIT Guwahati, Dr Anuj Nandi of URSC, ISRO, and Dr Sreehari Harikesh of the University of Haifa, Israel.
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