ISRO Reveals Insights on Black Hole Behavior Through QPO Research

BENGALURU: The Indian Space Research Organisation (ISRO) has recently unveiled significant findings regarding black hole behavior, particularly focusing on the black hole designated GRS 1915+105. The research team, composed of scientists from ISRO and academic institutions, announced their discoveries on July 25, 2025, emphasizing the unique fluctuations in X-ray brightness observed from this celestial body. These fluctuations alternate between low-brightness ('dips') and high-brightness ('non-dips') phases, each lasting several hundred seconds. Notably, during the high-brightness phases, rapid flickers in X-rays were detected at a frequency of approximately 70 times per second, a phenomenon referred to as Quasi-periodic Oscillations (QPOs). This behavior was found to be absent during the low-brightness phases.

The research was conducted by a team that includes Anju Nandi from ISRO, Santabrata Das and Seshadri Majumder from the Indian Institute of Technology (IIT) Guwahati, and Sreehari H from Hafiza University. Their findings suggest that these rapid QPOs are closely linked 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 most prominent, the corona is observed to become more compact and significantly hotter, resulting in increased luminosity. Conversely, during the dimmer phases, the corona expands and cools, leading to the disappearance of the flickers.

The research was published in the peer-reviewed journal Monthly Notices of the Royal Astronomical Society on July 4, 2025. The study titled "Evidence of oscillating ‘compact’ Comptonised corona in GRS 1915+105: insights into HFQPOs with AstroSat" indicates that the compact oscillating corona is likely the origin of the fast QPO signals observed.

ISRO's AstroSat, India’s first dedicated multi-wavelength space observatory, has been continuously monitoring GRS 1915+105 since its launch in September 2015. The observatory aims to provide deeper insights into the behavior of black holes and the extreme conditions present in their vicinity. According to Dr. Anju Nandi, leading researcher at ISRO, these findings are pivotal for scientists seeking to comprehend the dynamics occurring around black holes, where gravitational forces are immensely strong and conditions are radically extreme. This research not only enhances our understanding of black holes but also contributes to the broader field of astrophysics by shedding light on the complex interactions between matter and gravity in extreme environments. The implications of these findings may extend to future research endeavors aimed at exploring the mysteries of black holes and their formation processes.

In summary, ISRO's recent discoveries regarding the behaviors of black holes, particularly GRS 1915+105, through the observation of QPOs and the dynamic characteristics of the corona mark a significant advancement in astrophysical research. This work underscores the importance of continuous monitoring and research in unraveling the complexities of the universe's most enigmatic phenomena.