IIT Guwahati-led team spots rapid X-ray flickers from distant black hole, unlocking clues to cosmic mysteries

Syllad | The Rising MeghalayaAugust 18, 2025

A multi-institutional team of scientists, including researchers from IIT Guwahati, ISRO’s U. R. Rao Satellite Centre, and Haifa University, Israel, has decoded a puzzling X-ray signal pattern from the black hole GRS 1915+105, located about 28,000 light-years from Earth.

Using India’s space observatory AstroSat, the team discovered that the black hole’s X-ray brightness swings between bright and dim phases lasting several hundred seconds. Strikingly, during the bright phases, the researchers detected rapid X-ray flickers repeating nearly 70 times per second (∼70 Hz)—a phenomenon that vanishes when the system shifts to its dimmer mode.

“This is the first clear evidence of such fast flickering tied to the high-brightness phases,” said Prof. Santabrata Das, Department of Physics, IIT Guwahati. “AstroSat’s unique capabilities allowed us to uncover how these flickers disappear once the system cools and dims.”

The study shows that the corona, the superheated region surrounding the black hole, changes drastically with brightness. In bright phases, the corona becomes hotter and more compact, fueling rapid flickers. In dimmer phases, it expands and cools, shutting the flickers off. This dynamic behaviour reveals that the corona is not a fixed structure but a shifting, oscillating environment.

“This direct link between corona modulations and X-ray flickering brings us closer to understanding how black holes regulate energy flow,” added Dr. Anuj Nandi, U. R. Rao Satellite Centre, ISRO.

The findings deepen scientific understanding of the extreme gravitational forces and high-energy processes near black holes, offering fresh insights into how they grow, release energy, and influence the evolution of galaxies.

The results were published in the journal Monthly Notices of the Royal Astronomical Society, co-authored by Prof. Santabrata Das and research scholar Seshadri Majumder (IIT Guwahati), Dr. Anuj Nandi (ISRO), and Dr. Sreehari Harikesh (University of Haifa, Israel).