ISRO–IIT-Guwahati team detects rapid X-ray flickers from distant black hole, revealing new cosmic insights

Researchers from the Indian Space Research Organisation (ISRO) and the Indian Institute of Technology (IIT) Guwahati, in collaboration with Haifa University, Israel, have uncovered a distinctive pattern of X-ray signals emitted by a black hole nearly 28,000 light-years away.

The discovery, made using India’s multi-wavelength space observatory AstroSat has been published in the Monthly Notices of the Royal Astronomical Society and is being hailed as a breakthrough in black hole research.

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The stellar-mass black hole, known as GRS 1915+105, has long intrigued astronomers because of its extreme variability and high-energy emissions.

Using AstroSat’s precision instruments, the team observed that the object’s X-ray brightness oscillates between bright and dim phases, each lasting several hundred seconds.

Remarkably, during the bright phase, the black hole produced rapid X-ray flickers repeating 70 times per second (70 Hz)—signals that vanished entirely during the dim phase.

“This is the first time we have direct evidence linking such rapid flickering to changes in the corona—the hot plasma surrounding the black hole,” explained Dr Anuj Nandi of ISRO’s U. R. Rao Satellite Centre.

The corona, a region of superheated particles above the accretion disk, plays a critical role in shaping a black hole’s radiation. The study revealed that during bright phases, the corona becomes compact and hotter, producing intense flickers. In dim phases, it expands and cools, suppressing the signals.

“This shows the corona is not a static structure but a dynamic one that changes with the inflow of gas spiralling into the black hole,” said Prof Santabrata Das of IIT Guwahati.

Once considered simple gravitational traps, black holes are now recognized as powerful engines of energy that influence galaxy evolution.

Their accretion disks and coronas can drive outflows and jets that regulate star formation in their host systems. The detection of these X-ray flickers from GRS 1915+105 provides fresh insights into how energy is released near the event horizon under conditions of extreme gravity and heat.

Launched in 2015, AstroSat has been central to advancing India’s role in high-energy astrophysics. Its ability to observe the universe across multiple wavelengths has enabled discoveries ranging from binary star systems to galaxy clusters.

This latest finding highlights how India’s indigenous space observatory is making significant contributions to global astrophysical research.

“This study reshapes our understanding of black hole dynamics and the extreme environments they create,” the researchers concluded. “It also opens up new avenues for probing how black holes grow and influence their cosmic neighbourhoods over billions of years.”