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Curated by RSF Research Staff

A new approach to measure the mass of intergalactic black holes

Researchers suggested that among bright X-ray flares that continue for a few years, some can be caused by tidal gravitational disruption of a star which passed too close to a super massive black hole.

Astronomers think, if a star passes within the tidal radius of a black hole then the gravity rips the star apart. As the stellar remnant approaches a black hole, its gravitational potential energy is converted into heat through viscous effects. Some of the debris can be ejected, while the remaining part can be ingested by a central super massive black hole. In this case the accretion flow reaches a temperature of about 105K and emits brightly at optical, ultraviolet, and X-ray wavelengths during the period from about 100 days to a few years.

A tidal disruption event is an astronomical phenomenon in which a previously dormant black hole destroys a star passing too close to its central part.

This kind of event are very difficult to capture and one of them is the Swift J1644+57. It is the result of a truly extraordinary event -- the awakening of a distant galaxy's dormant black hole as it shredded and consumed a star. The galaxy is so far away, it took the light from the event approximately 3.9 billion years to reach Earth.

This illustration highlights the principal features of the event Swift J1644+57 (tidal disruption of a star by a supermassive black hole) and summarizes what astronomers have discovered about it. Credit: NASA’s Goddard Space Flight Center.

Recently, a team led by Elena Seifina found something interesting while looking at the event called “Swift J1644 + 57”. They observed a gamma-ray burst similar to those coming from remote galaxies in the hardest range of the electromagnetic spectrum. But this time it was slightly different so they suspected that they were observing the tidal destruction of the star by a supermassive black hole. Not only, their new idea permitted them to discover a new black hole, but they were able to propose a new approach to measure its mass thanks to the observation of the accretion disk formed around it.

"Calculations showed that Swift J1644 + 57 contained a supermassive black hole with a mass of 7×106 solar masses. This is an object that we do not see, but which provides high luminosity due to its strong gravitational field and an accretion disk around it."

Elena Seifina, CNRS, France.

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