GUWAHATI: A collaborative research effort involving the Indian Institute of Technology Guwahati (IIT Guwahati), U.R. Rao Satellite Centre (ISRO), the University of Mumbai, and the Tata Institute of Fundamental Research (TIFR) has made significant strides in understanding black hole binaries. Using data from AstroSat, India’s space astronomy observatory, the team has unveiled intriguing X-ray characteristics of a newly discovered black hole binary system, Swift J1727.8-1613.
Direct observation of black holes remains one of the most challenging feats in astronomy, as their intense gravitational pull prevents anything, including light, from escaping. However, black hole binary systems, where a black hole is gravitationally paired with another object like a star, offer a rare window for study.
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In these systems, the black hole siphons materials from its companion star, creating an accretion disk of gas and dust. As this material spirals into the black hole, it heats up and emits X-rays, which can be detected and analysed using space-based telescopes.
AstroSat, equipped with advanced instruments for observing the universe in multiple wavelengths, is uniquely suited to study such high-energy phenomena. The research team, led by Prof. Santabrata Das from IIT Guwahati, focused on the black hole binary system Swift J1727.8-1613.
Their study revealed crucial insights into the system’s behaviour, particularly through the detection of Quasi-periodic Oscillations (QPOs) in the X-ray light emitted from the accretion disk. “QPOs are indispensable for investigating mysterious black hole systems,” stated Das.
“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 neighboring environment,” Das added.
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QPOs represent the flickering of X-ray light at specific frequencies from astronomical objects. In the case of Swift J1727.8-1613, the team observed these oscillations change frequency from 1.4 to 2.6 times per second over just seven days, in extremely high-energy X-rays, which are approximately a billion degrees hot.
The discovery of these QPOs has profound implications for astrophysics. They offer a powerful tool to probe the inner regions of accretion disks around black holes, determine black hole masses and spin periods, and test Einstein's theory of general relativity. This theory describes gravity as a curvature of spacetime around massive objects like black holes, dictating the paths that accreting matter will follow.
