Super-massive black holes weigh thousands to millions of Suns and are thought to reside at the heart of all galaxies, including the Milky Way. Stellar black holes, resulting from the gravitational collapse of a single star, are more modest in weight, on the order of 10 solar masses.
Jerome Orosz, an astronomer from San Diego State University, and his team pointed their telescope in the direction of an X-ray source in the spiral galaxy Messier 33, which is 3 million light years away. There they found a stellar black hole and a companion star that passes directly in front of it on a three-and-a-half-day orbit, eclipsing the black hole's X-ray emissions. This allowed the team to calculate the pair's masses more accurately than usual.
The black hole was found to weigh 15.7 solar masses, making it the biggest stellar black hole ever found. It still pales in comparison to the size of its companion star. At 70 solar masses it is the most massive star found in a binary system with a black hole.
"This is a huge star that is partnered with a huge black hole," said co-author Jeffrey McClintock of the Harvard-Smithsonian Centre for Astrophysics. The discovery is even more remarkable because current astronomical models have difficulty predicting anything greater than ten solar masses.
The research appeared today in the British journal Nature.
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