IIT Guwahati, ISRO detect mysterious X-Ray signal from distant black hole

Guwahati, Aug 21: Researchers at the Indian Institute of Technology (IIT) Guwahati, in collaboration with the UR Rao Satellite Centre (URSC) of ISRO and the University of Haifa, Israel, have uncovered a mysterious X-ray signal pattern emitted from a black hole called GRS 1915+105, located nearly 28,000 light years from Earth.

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

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.

Speaking about the key findings of the research, Prof Santabrata Das of the Department of Physics of IIT Guwahati, said, “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 phase, when the flickers are strongest, the corona becomes more compact and significantly hotter. In contrast, during the dimmer phase, 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,” Prof Das said.

He said 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,” Prof Das said.

Speaking about the significance of the research, Dr Anuj Nandi of URSC, ISRO, said, “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.”

The findings of this research have been published in the journal Monthly Notices of the Royal Astronomical Society in a paper co-authored by Prof Das and his research scholar Seshadri Majumder, along with Dr Nandi, and Dr Sreehari Harikesh of the University of Haifa, Israel.

By

Staff Reporter