WASHINGTON (AFP) - US astronomers have discovered the biggest black hole orbiting a star 1.8 million light-years from Earth in the constellation Cassiopeia, with a record-setting mass of 24 to 33 times that of our Sun, NASA said Tuesday.

The massive newcomer beats the previous stellar-mass black hole discovered October 17 in the M33 galaxy that has 16 times the mass of our Sun, the US space agency said.

Like the much larger, supermassive black holes found at galaxy centers, stellar-mass black holes have such powerful gravity fields that not even light can escape them. Astronomers estimate their mass by measuring their gas emissions and the gravitational effect on the stars they orbit.

"We weren't expecting to find a stellar-mass black hole this massive," says Andrea Prestwich of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

Lead author of the discovery paper in the November 1 Astrophysical Journal Letters, Prestwich and his team found the new stellar-mass black hole using NASA's Chandra X-ray Observatory.

"We now know that black holes that form from dying stars can be much larger than we had realized," he added.

Prestwich's team was able to measure the black hole's mass because it has an orbiting companion: a hot, highly evolved star. The star is ejecting gas in the form of a wind.

Some of this material spirals toward the black hole, heats up, and gives off powerful X-rays before crossing the point of no return.
US astronomers spot massive, record-setting stellar-mass black hole - Yahoo! News
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