BENGALURU: 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 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 (frequency 〖ν〗_(QPO) ∼70 Hz), 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 source's behaviour.
Explaining what causes the mysterious fast flickers, the research team in the report 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 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’ Comptonized corona in GRS 1915+105: insights into HFQPOs with AstroSat- was also been published in the journal, Monthly Notices of Royal Astronomical Society on July 4, 2025. ISRO shared the details on July 25.
The research team noted that these findings will help scientists understand what happens in the vicinity of a black hole, where gravity is incredibly strong and conditions are extreme. "Indeed, GRS 1915+105 acts as cosmic laboratory, and with AstroSat's remarkable contributions, Indian scientists are decoding the ‘whispers’ of this black hole," the report stated.
Black holes are termed to be the universe's most enigmatic powerhouses. They cannot be seen directly, but their immense gravity reveals their presence. Born from the collapse of massive stars that exhaust their fuel, these cosmic voids are invisible because not even light can escape their grasp.
However, a black hole in a binary system with a companion star, triggers a dramatic process known as accretion, pulling in stellar material that spirals inward and heats up to over 10 million degrees (far hotter than the Sun's surface temperature of 6000 degrees). This super-heated matter emits intense X-rays, which are captured by space telescopes, offering scientists a rare window into the otherwise hidden lives of black holes.
In a distant corner of our galaxy (nearly 28000 light-years away) lies the GRS 1915+105. This intriguing black hole X-ray binary system, consists of a rapidly rotating black hole with a mass about 12 times that of a Sun and its companion star, has captured the attention of scientists due to its unusual and dynamic behaviour. A schematic diagram of the complex accretion process around GRS 1915+105, forming a swirling disc (1-10 million degree) and corona (∼100 million degrees) structure, is depicted, explained the scientists' team.