A groundbreaking study conducted by a multi-institutional research team has shed new light on the dynamics of black hole binary systems. The team, comprising experts from the Indian Institute of Technology (IIT) Guwahati, U. R. Rao Satellite Centre (URSC), ISRO, University of Mumbai, and Tata Institute of Fundamental Research (TIFR), utilized data from AstroSat, India’s premier space astronomy observatory, to investigate a newly discovered black hole binary system named Swift J1727.8-1613.
The study reveals significant findings on the X-ray characteristics of black holes, which are typically elusive due to their nature. Black hole binaries, where a black hole pairs with another object such as a normal star, offer a unique window into studying these mysterious entities. In these systems, material from the companion star forms an accretion disk around the black hole, heating up and emitting X-rays as it spirals inward. These X-rays, detectable by space-based telescopes like AstroSat, provide crucial data on black hole properties.
AstroSat, India’s first dedicated space observatory, orbits Earth equipped with instruments that observe the universe in multiple wavelengths, including X-rays. This capability makes it an ideal tool for studying high-energy phenomena like black hole binaries.
Prof. Santabrata Das from IIT Guwahati emphasized the importance of their findings, stating, “QPOs are indispensable for investigating mysterious black hole systems. By examining the periodic variations of X-ray photons at high energies (around 100 keV), QPOs help decode the footprints of a black hole’s strong gravity. This aids in understanding their fundamental properties and the dynamics of how the black hole attracts matter from the neighboring environment.”
The team discovered Quasi-periodic Oscillations (QPOs) in the X-ray light emitted by Swift J1727.8-1613’s accretion disk. These QPOs, which represent flickering X-ray light at specific frequencies, shifted from 1.4 to 2.6 times per second over just seven days. This frequency change was observed in extremely high-energy X-rays, which are generated at temperatures around a billion degrees.
Dr. Anuj Nandi from URSC/ISRO highlighted the significance of these observations, saying, “Unique capabilities of AstroSat, namely the high time resolution and large X-ray photon collecting area, made the discovery of evolving QPO frequency in high energy X-rays possible. These high energy X-rays are generated when low energy photons interact with hot material from inner disk around black holes via Compton scattering process. AstroSat observations distinctly confirm that Swift J1727.8−1613 was in an accretion state dominated by Comptonized emissions that manifest aperiodic modulation, resulting in observed QPO features.”
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This discovery has profound implications for understanding the inner regions of accretion disks, determining the masses and spin periods of black holes, and testing Einstein’s theory of general relativity. According to this theory, massive objects like black holes warp the fabric of spacetime around them, influencing the paths of accreting matter.
The findings have been published in the prestigious Monthly Notices of the Royal Astronomical Society. The paper is co-authored by Prof. Santabrata Das from IIT Guwahati, Dr Anuj Nandi from URSC/ISRO, Prof. H. M. Antia from the University of Mumbai, Dr Tilak Katoch and Mr Parag Shah from TIFR, along with research student Mr Seshadri Majumder from IIT Guwahati.
For a more detailed insight into the study, a video byte is available here.
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