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M87 Cluster

April 25, 2015

One of the biggest black holes in the universe seems to have fired a bullet into the intergalactic void. And it’s moving more or less in our direction at record speed.

The fast-moving bullet is a star cluster in the constellation Virgo, which is low in the southeastern sky at nightfall. The cluster lies in the same direction as M87, an elliptical galaxy that’s much bigger and heavier than our own galaxy, the Milky Way.

An enormous black hole inhabits the center of M87. It’s almost seven billion times more massive than the Sun — one of the heaviest black holes yet measured. The star cluster may have passed close to the black hole, whose powerful gravity hurled it away.

Like most galaxies, M87 is moving away from us. Astronomers see this because as the galaxy’s light waves travel toward us, the expanding universe stretches those waves to longer, redder wavelengths, producing a so-called redshift.

But the star cluster doesn’t have a redshift. Instead, it has a blueshift, which means it’s moving toward us. Moreover, it’s racing toward us faster than any known star, star cluster, or galaxy — more than two million miles per hour.

The cluster isn’t a danger to the Milky Way, though. It’s moving at a tangent to our galaxy, so it won’t hit us. Instead, it’s a celestial record breaker, likely owing its superlative qualities to a superlative black hole at the heart of a giant galaxy.


Script by Ken Croswell, Copyright 2015

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