Skywatch

  • December 15, 2005

    Episode 14: Andromeda's Black Hole

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    Scientists believe that gigantic black holes exist in the centers of most galaxies, but only two had actually been confirmed. Now we can bring that number to three. Our neighbor galaxy, Andromeda, was long thought to harbor a black hole at its center. Its core gives off X-rays, the likely product of a disk of gas spiraling into a black hole. But the core also emits a mysterious blue light, a fact known for some time but never really understood. Scientists using the Hubble Space Telescope Imaging Spectrograph solved the puzzle. The blue glow comes from a flat disk of more than 200 young, hot stars very close to the galaxy's core. All these stars so close to the core is evidence that Andromeda, also known as M31, harbors a black hole twice as large as originally thought. It would contain 140 times the amount of material in our Sun.