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This NASA handout artist's illustration recieved 31 October 2007 shows the IC 10 X-1 system, the black hole lies at the upper left and its companion star is on the right. The two objects orbit around a center of gravity once every 34.4 hours. 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 30 October 2007.The stellar companion is a type known as a Wolf-Rayet star. Such stars are highly evolved and destined to explode as supernovae. The black hole companion is shedding its outer envelope in a powerful wind, and some of this gas is captured by the black hole’s powerful gravity.