IIT Guwahati, Isro scientists decode flickering X-rays from black hole

Researchers at the Indian Institute of Technology (IIT), Guwahati, in collaboration with UR Rao Satellite Centre, ISRO and Haifa University, Israel, have uncovered a mysterious X-ray signal pattern emitted from a blackhole, located nearly 28,000 light-years from the Earth, according to officials.

Using the data from India's space observatory AstroSat, the researchers observed the X-ray brightness from the black hole alternated between bright and dim phases, each lasting several hundred seconds, they said.

The findings of this research have been published in the prestigious journal, Monthly Notices of the Royal Astronomical Society.

Researchers from across the world are working towards understanding the phenomena of black holes. While drawing gas from the outer layers of their companion stars, they produce extreme heat and emit X-rays. By studying these X-rays, scientists can learn about the environment near the black hole.

According to Santabrata Das, Professor at the Department of Physics, IIT Guwahati, "We have found the first evidence of rapid X-ray flickering, repeating nearly 70 times per second, 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 researchers observed that the X-ray brightness from the targeted black hole alternated between two distinct phases -- one bright and one dim. During the brighter phases, when the flickers are strongest, the corona becomes more compact and significantly hotter. In contrast, during the dimmer phases, it expands and cools, causing the flickers to disappear.

"This clear correlation points to the compact, oscillating corona as the likely source of these fast signals. While each phase lasted several hundred seconds and repeated in a regular pattern, a rapid flickering signal appeared only during the bright phase. This discovery shows that the corona around the black hole is not a fixed structure and changes its shape and energy depending on how gases flow into the black hole," he added.

Das explained that the research provides a deeper understanding of the extreme gravitational intensity and high temperature that exist near a black hole's edge. These findings also improve our models of how black holes grow, release energy and affect their surroundings. It also offers clues to how black holes may influence the evolution of entire galaxies.

Anuj Nandi, URSC, ISRO added, "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.