Black holes are believed to lurk at the center of all massive galaxies throughout the Universe and are inextricably linked to the properties of their host galaxies. So, revealing more about these giants could be the key to understanding how galaxies evolve over time.
The gravity of a black hole is extreme and can destroy stars that come too close. The debris from these torn stars spirals inward toward the hole, heats up, and emits intense X-rays.
Despite the number of black holes thought to exist in the cosmos, many are dormant - there is no falling material to emit detectable radiation - and therefore difficult to study. However, every few hundred thousand years or so, a star is predicted to pass close enough to a particular black hole to be torn apart. This offers a brief window of opportunity to measure some fundamental properties of the hole itself, such as its mass and the rate at which it is rotating.
"It's very difficult to restrict the spin of a black hole because spin effects only come up very close to the hole itself, where gravity is intensely strong and it's hard to see clearly," said Dheeraj Pasham of the MIT Kavli Institute for Astrophysics and Space Research in Massachusetts, USA, and lead author of the new study.
“However, models show that the mass of a fragmented star settles into a kind of inner disk that emits X-rays. We guessed that finding instances where this disk glows especially brightly would be a good way to restrict the rotation of a black hole, but observations of such events weren't sensitive enough to explore this region of strong gravity in detail - until now. ”
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IMAGE: (Image of the host galaxy of ASASSN-14li in comments) The cosmic source called ASASSN-14li, hiding a black hole at least a million times more massive than the Sun that destroyed and devoured a nearby star, seen by Europeans Photon Imaging Camera (EPIC) at ESA's XMM-Newton X-ray Observatory.
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