IIT Guwahati, ISRO study reveals dynamic corona around black hole

Scientists from IIT Guwahati, in partnership with ISRO’s U R Rao Satellite Centre and Haifa University in Israel, have detected a rare X-ray pattern coming from a distant black hole using India’s AstroSat observatory.

The black hole, GRS 1915+105, is located nearly 28,000 light-years away and was found to emit X-rays that shifted between bright and faint phases lasting several minutes each.

Researchers said this discovery offers valuable clues to how black holes release energy and interact with their surroundings.

Professor Santabrata Das of IIT Guwahati explained, “We have 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. Interestingly, these fast flickers disappear during the low-brightness phases. This new understanding was made possible by AstroSat’s powerful, unique observational capabilities.”

The analysis showed that during brighter phases, the corona, the hot cloud of gas around the black hole, becomes smaller and hotter, producing the rapid flickers. When the corona expands and cools in dimmer phases, the flickering vanishes.

Researchers concluded that the corona is not a stable structure but changes shape and energy depending on how gas flows into the black hole.

The rapid flickers were observed only during bright phases, making this the first evidence that the oscillating corona is directly tied to the phenomenon.

“Our study provides direct evidence for the origin of X-ray flickering. We have found that this flickering is linked to modulations in the corona surrounding the black hole,” said Dr Anuj Nandi from URSC, ISRO.

The work, published in the “Monthly Notices of the Royal Astronomical Society,” was carried out by Prof Das and his doctoral scholar Seshadri Majumder, along with Dr Nandi and Dr Sreehari Harikesh of Haifa University.

According to the researchers, these findings help refine scientific models of how black holes grow and emit radiation.

The results also highlight how black holes may regulate energy and matter in galaxies, shaping their long-term evolution.