Finding the Mama Bear of Black Holes

While astronomers have studied both big and little black holes for decades, evidence for those middle-sized black holes has been much harder to come by. Now, astronomers at NASA's Goddard Space Flight Center in Greenbelt, Md., find that an X-ray source in galaxy NGC 5408 represents one of the best cases for a middleweight black hole to date. "Intermediate-mass black holes contain between 100 and 10,000 times the sun's mass," explained Tod Strohmayer, an astrophysicist at Goddard. "We observe the heavyweight black holes in the centers of galaxies and the lightweight ones orbiting stars in our own galaxy. But finding the 'tweeners' remains a challenge."
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