This pattern suggests that the compact oscillating corona seems to be the origin of these fast QPO signals.
A team of scientists and researchers from the Indian Space Research Organisation (ISRO) on Friday listed out their unique findings while studying the Black Hole as part of their study.They noted that the X-ray brightness from the fascinating and mysterious black hole, GRS 1915+105, fluctuates dramatically over time. It exhibits a unique pattern of alternating low-brightness (‘dips’) and high-brightness (‘non-dips’) phases, each lasting a few hundred seconds.
During the high-brightness phase, the team discovered that the rapid flickers in X-rays were repeating about 70 times per second, known as Quasi-periodic Oscillations (QPOs). Interestingly, such ‘fast’ flickers vanish during the low-brightness phase, noted the researchers Anju Nandi from ISRO, Santabrata Das from IIT- Guwahati, Sreehari H from Hafiza University and Seshadri Majumder from IIT Guwahati.
India’s first dedicated multi-wavelength space observatory, AstroSat, has been continuously monitoring the black hole GRS 1915+105 since its launch in September 2015 and is working to provide insights into the source’s behaviour. The research team stated that they found that these rapid QPOs are intimately connected to a super-heated cloud of energetic plasma surrounding the black hole, known as the corona. During the bright, high-energy phases when QPOs are strongest, the corona becomes more compact and significantly hotter with higher luminosity. Conversely, in the dimmer dip phases, the corona expands and cools, causing the flickers to vanish. This pattern suggests that the compact oscillating corona seems to be the origin of these fast QPO signals.
This research work titled- Evidence of oscillating ‘compact’ Comptonised corona in GRS 1915+105: insights into HFQPOs with AstroSat- was also published in the journal Monthly Notices of the Royal Astronomical Society, on July 4, 2025. ISRO shared the details on July 25.
Source : https://www.newindianexpress.com/states/karnataka/2025/Jul/26/isro-shares-new-findings-on-black-hole
