BRIDGEPORT, WV (S-M) - Astronomers announced recently that they have found the most massive known stellar black hole.


The black hole is in the dwarf galaxy IC-10, which is only about 2 million light years from Earth in the constellation Cassiopeia. It is thought that the black hole is orbited by a companion star, which passes in front of the black hole, periodically blocking the hole's X-rays. "By observing the periodic dimming, the scientists were able to determine the orbit of the companion, and the mass of the two bodies," said Associate Editor Floyd Cummins.


With a mass of 24-33 times the Sun, the newly found object smashes all previously known records for stellar black holes. "These holes are different from the giants at the center of galaxies," said Cummins. "These stellar black holes form during the death of a star. Usually, it is expected that a dying star will throw off much of its mass before a black hole forms. How this hole managed to retain so much mass is something of a mystery."


One theory involves a possible scarcity of heavy elements in the star from which the hole was born. "Heavy elements get more of a push on their electrons from radiation pressure inside a star," said Cummins. "The outgoing light literally carries away some of the mass. If the star did not have much of the heavy elements, the light would not have been able to push out much mass, and such a heavy black hole could form. The hole is in an entire galaxy which is lacking in heavy elements, so this theory definitely fits what we observe."


Scientists lauded the discovery. "We weren’t expecting to find a stellar-mass black hole this massive," said Andrea Prestwich of the Harvard-Smithsonian Center for Astrophysics. "It seems likely that black holes that form from dying stars can be much larger than we had realized." - GW

Copyright 2007 Starry Mirror and Glen Ward

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Dwarf galaxy IC-10 is home to the newly found black hole.  (NASA)

In this artist's conception, gas and dust spiral into the massive black hole. (NASA)