A significant discovery has been made about black holes using the unique abilities of Indian Space Research Organisation’s (ISRO) AstroSat. The satellite, orbiting 650 km above the surface of our planet, has detected aperiodic modulation of high-energy X-ray photons (elementary particles of the electromagnetic field that move at the speed of light in a vacuum). The discovery was made during what is termed an unusual outburst phase from a black hole binary named J1727.8-1613 discovered in August last year. A black hole binary is a system of two black holes in close orbit around each other.

In a Black Hole X-ray Binary (BH-XRB), one black hole pulls matter from its deformed companion, leading to the formation of a luminous disk that forms gradually. As matter accretes through the luminous disk it reaches temperatures in the millions of degrees and starts emitting high-energy X-rays, leading to the detection of the black hole system. BH-XRBs are critical to the understanding of the minute processes that govern accretion dynamics, providing a window to understand important mechanisms in extreme environments.

It was revealed that the aperiodic modulation led to Quasi-Periodic Oscillation (QPO) at a fixed frequency but in a short span of a week it evolved from 1.4 Hz to 2.6 Hz. This is the first time such a phenomenon has been seen in a Bh-XRB. The study also reveals that high energy (or hard) X-rays are made from soft X-rays through the accretion disk by ‘hot’ electrons. It is important to study QPOs as they help us decode the black holes and help us better understand the properties of accretion dynamics.

AstroSat is a multi-wavelength space telescope that can see in visible, near and far Ultraviolet spectrum. It also has the equipment to detect hard and soft X-rays. Data from the International Space Station was also used in the study.

The study has been reported in the Monthly Notices of the Royal Astronomical Society (MNRAS) by the U R Rao Satellite Centre of ISRO, Indian Institute of Technology Guwahati (IITG), University of Mumbai, and Tata Institute of Fundamental Research (TIFR).

(With Agency Inputs)