GUWAHATI: A multi-institutional research team, including the Indian Institute of Technology (IIT) Guwahati, has made significant strides in understanding black holes through the study of a newly discovered black hole binary system – Swift J1727.8-1613.
Utilising data from AstroSat, India’s first dedicated space astronomy observatory, the team uncovered intriguing X-ray characteristics that could provide deep insights into black hole dynamics.
During their study, the researchers detected Quasi-periodic Oscillations (QPOs) in the X-ray light emitted by the accretion disk of Swift J1727.8-1613.
QPOs, flickering X-ray light from an astronomical object at specific frequencies, were observed to change frequency from 1.4 to 2.6 times per second over just seven days.
This variation was noted in extremely high-energy X-rays, which are incredibly hot, around a billion degrees.
“QPOs are indispensable for investigating mysterious black hole systems,” explained Prof. Santabrata Das from IIT Guwahati’s Department of Physics.
“By examining the periodic variations of X-ray photons at high energies, 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 neighbouring environment,” he added.
The team also comprised researchers from UR Rao Satellite Centre (ISRO), University of Mumbai, and Tata Institute of Fundamental Research (TIFR).
Black holes are notoriously difficult to study directly due to their nature, as they emit no light or radiation detectable by current instruments.
However, black hole binaries, where a black hole is paired with another celestial object such as a normal star, offer a unique investigative opportunity.
In these systems, the black hole’s gravitational pull attracts material from its companion star, forming an accretion disk of gas and dust.
As this material spirals closer to the black hole, it heats up to millions of degrees and emits X-rays, which can be detected by space-based telescopes.
The implications of this discovery are substantial. QPOs allow astronomers to study the inner regions of accretion disks, determine the masses and spin periods of black holes, and test Einstein’s theory of general relativity.
This theory posits that massive objects like black holes warp the fabric of spacetime, influencing the paths of accreting matter.
Highlighting the significance of the findings, Dr. Anuj Nandi from the UR Rao Satellite Centre (ISRO) noted, “The unique capabilities of AstroSat, namely its 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 the inner disk around black holes via Compton scattering. AstroSat observations distinctly confirm that Swift J1727.8-1613 was in an accretion state dominated by Comptonised emissions that manifest aperiodic modulation, resulting in observed QPO features.”
The details of this research have been published in the prestigious journal, Monthly Notices of the Royal Astronomical Society.
The paper is co-authored by Prof Das from IIT Guwahati, Dr Nandi from U R Rao Satellite Centre, ISRO, Prof. HM Antia from the University of Mumbai, Dr Tilak Katoch, and Parag Shah from TIFR, along with research student Seshadri Majumder from IIT Guwahati.
This study represents a significant advancement in our understanding of black hole systems and showcases the capabilities of India’s AstroSat in contributing to high-energy astrophysics research.
