A multi-institutional research team, including members from the Indian Institute of Technology Guwahati, UR Rao Satellite Centre (ISRO), University of Mumbai, and Tata Institute of Fundamental Research, has conducted a significant study on a newly discovered black hole binary system called Swift J1727.8-1613. Utilizing data from AstroSat, India's first dedicated space astronomy observatory, the team uncovered intriguing X-ray characteristics that offer potential insights into the nature of black holes.
According to a press release from IIT Guwahati, black holes are challenging to study directly due to their nature, which prevents anything from escaping, including light. However, black hole binaries, where a black hole is paired with another object such as a normal star, present a unique opportunity for investigation. In these systems, the black hole's gravity pulls material from its companion star, forming an accretion disk of gas and dust spiraling into the black hole. As this material is drawn closer, it heats up to millions of degrees, emitting X-rays that can be detected by space-based telescopes.
The research team, led by Prof Santabrata Das from the Department of Physics at IIT Guwahati, focused on these X-ray emissions using AstroSat's advanced instruments. "QPOs are indispensable for investigating mysterious black hole systems," said Prof Das. "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 the accretion disk of Swift J1727.8-1613. QPOs are flickerings of X-ray light from an astronomical object around specific frequencies. Remarkably, these QPOs shifted their frequency from 1.4 to 2.6 times per second over just seven days, observed in extremely high-energy X-rays, which are around a billion degrees hot.
"The implications of this discovery are profound," the press release stated. "QPOs can help astronomers study the inner regions of accretion disks and determine the masses and spin periods of black holes. They can also test Einstein's theory of general relativity, which describes gravity as a geometric property of space and time."
Dr. Anuj Nandi from UR Rao Satellite Centre, ISRO, highlighted the importance of AstroSat's capabilities in making this discovery possible. "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 the inner disk around black holes via the 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," Nandi explained.
The details of this groundbreaking work have been published in the prestigious journal, Monthly Notices of the Royal Astronomical Society. The paper is co-authored by Prof Santabrata Das from IIT Guwahati, Dr. Anuj Nandi from UR 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.
