Slimmed-Down Cluster

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Slimmed-Down Cluster

The giant families of stars known as globular clusters are like carnival rides: They do a lot of bobbing up and down. And they may lose a bit of themselves with every gyration.

An example is the cluster Messier 12. It’s probably more than 16,000 light-years from Earth. It contains a couple of hundred thousand stars, all packed into a ball about 75 light-years across. That means the stars are much closer together than the stars in our part of the galaxy.

Like all globulars, M12 travels at an angle to the Milky Way’s disk. So it periodically passes through the disk. During each pass, the gravity of the disk may pull away some of the stars on the outskirts of M12.

A study a couple of decades ago found a lack of lower-mass stars in the cluster. Heavier stars tend to congregate in a cluster’s core, where they’re held fast by the gravity of the other stars around them. Less-massive stars migrate to the outskirts, where they’d be easy to pull away.

Today, M12 contains about 200,000 stars. But it could have lost several times that number over its 13-billion-year lifetime. So as many as a million of the cluster’s stars might now be orbiting the center of the galaxy on their own — pulled away from their birthplace.

Messier 12 is in Ophiuchus, the serpent bearer, which is in the east and southeast at nightfall. But you need a telescope to see this possibly vanishing cluster of stars.

Script by Damond Benningfield

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