Theoretical physicists at the Indian Institute of Science (IISc) in Bangalore have unravelled new facts about black holes that are expected to have significant impact on understanding these cosmic bodies better. A black hole is a region of spacetime from which gravity prevents anything, including light, from escaping.
IISc researchers, Banibrata Mukhopadhyay and Indrani Banerjee for the first time established a correlation between two fundamental and important facets of black holes (BHs) — their mass and their spin.
Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is general consensus that supermassive black holes exist in the centers of most galaxies. The hole is called “black” because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics.
Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as light. Matter falling onto a black hole can form an accretion disk heated by friction, forming some of the brightest objects in the universe. Astronomers have identified numerous stellar black hole candidates in binary systems, and established that the core of our Milky Way galaxy contains a supermassive black hole of about 4.3 million solar masses.
Until the last decade, while the masses of several BHs had been determined independently through observation, there was no estimate of their spin. The IISc team has found that for a fixed accretion rate, the mass of BHs increases with the increasing spin, thus establishing a correlation between the two parameters for the first time.
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