Hercules powers into the sky late this evening. One of the constellation's best-known features is M13. It's a globular cluster -- a tightly packed ball of hundreds of thousands of stars.
A black hole may inhabit the center of the cluster -- one that's perhaps a thousand times as massive as the Sun, known as an intermediate-mass black hole.
In fact, globular clusters may be the breeding grounds for these black holes -- some of which may escape the clusters and roam through the galaxy.
These black holes probably form when smaller black holes merge in the centers of globular clusters.
If the merging black holes are about the same size, then they may stay put at the center of the cluster. But simulations by astronomers at Vanderbilt suggest that many of these black holes may get away. If the smaller black holes are of greatly different sizes, or if they're spinning at different rates, then a merger may kick them out of their parent cluster at millions of miles in hour.
The Vanderbilt work says that most of the Milky Way's 200 or so globulars should have given birth to at least one intermediate-mass black hole. And almost all of them should have been shot out into space. Today, they patrol the galaxy alone.
Hercules climbs into the northeast in late evening. Look for a lopsided square of stars called the Keystone. M13 is along the side of the Keystone that rises first, and is easily visible through binoculars.
Script by Damond Benningfield, Copyright 2008
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