In the constellation Hydra
31 million times the mass of the Sun
Diameter larger than the orbit of Mercury
Detection of an accretion disk
Although a black hole itself is invisible to the outside universe, many black-hole systems produce copious amounts of X-rays or ultraviolet radiation. That is because disks of superhot gas encircle the black holes. In the case of a star-sized black hole, the gas usually comes from a nearby companion star; the black hole's powerful gravity pulls gas off the surface of the star. In the case of a supermassive black hole, the gas comes from large clouds of gas in the crowded core of a galaxy, or from stars that pass close to the black hole and are torn apart by its gravitational pull. As the gas spirals into the black hole, it forms a wide, flat "accretion disk." The gas moves faster and faster as it spirals closer, so it's heated to millions of degrees. At such temperatures, the gas radiates most strongly in ultraviolet or X-ray wavelengths. These wavelengths are blocked by Earth's atmosphere, so only telescopes in space can detect them.
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This document was last modified: March 14, 2012.