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Doomed Pleiades

November 17, 2016

The Pleiades is doomed. By the time the star cluster completes another turn around the galaxy, it will have fallen apart, with its stars going their separate ways.

The Pleiades is the most famous of all clusters. Right now, it’s in good view in the east by about 7 p.m., above Aldebaran, the bright orange eye of Taurus the bull. It looks like a small but bright dipper.

In addition to the half-dozen bright stars that are easily visible to the eye, the cluster contains several thousand fainter stars. All of them were born together more than a hundred million years ago, from a huge cloud of gas and dust. Today, they move through space as a family, bound by their mutual gravitational pull.

As the Pleiades moves around the galaxy, though, it’ll begin to fall apart. Close encounters between member stars will fling some of them out of the cluster. And the gravitational field of the rest of the galaxy will slowly pull stars on its outskirts away from its denser core.

None of this happens instantly, though. It’ll probably take about 250 million years for the Pleiades to disintegrate — about the length of a single orbit around the center of the Milky Way.

Even then, most of the stars of the Pleiades will continue to move through the galaxy at the same speed and in the same direction. So even though the family will have fallen apart, it’ll be pretty easy to tell which stars were once members of this impressive cluster.

More tomorrow.


Script by Damond Benningfield

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