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Off-Center Black Hole

August 14, 2010

Everything about the galaxy M87 is big. The galaxy is a million light-years in diameter, and it contains a million million stars. And the black hole in its core is several billion times the mass of the Sun -- one of the largest black holes yet discovered.

But recent observations show that something has pushed this monster out of position. It's about 30 light-years away from where it should be, which is at the exact gravitational center of the galaxy.

On that kind of scale, 30 light-years isn't much. But the black hole is so "heavy" that it should settle right in the middle of M87. Since it's offset a bit, something must have pushed it out of position.

One possibility is a "jet" of particles from the disk of hot gas around the black hole. Like any other jet, it would produce thrust, pushing on the black hole. But the jet from M87's black hole doesn't seem powerful enough to move the black hole that far.

Instead, the researchers who found the offset think it's the result of a merger of two smaller black holes. As the black holes came together, they shoved each other away from the center. If so, then over time the black hole should settle in the center -- right where it belongs.

M87 is the largest member of a collection of galaxies known as the Virgo Cluster. Virgo's brightest star, Spica, is to the right of the Moon this evening. M87 is a good bit farther along that same line. But you need a telescope to see it.

Script by Damond Benningfield, Copyright 2010

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