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Faintest Cluster

October 4, 2015

The Sun travels through space alone, unaccompanied by any other star. But many stars belong to large clusters that contain hundreds or thousands of stars. Astronomers recently discovered a star cluster with two distinctions: It’s the faintest ever seen, and the galaxy is tearing it apart.

The newfound star cluster is about 65,000 light-years away. In fact, it’s far outside the Milky Way galaxy’s bright disk, which is home to our own solar system. Instead, Kim 1 is in the enormous halo that surrounds the disk. The cluster is in Pegasus, the flying horse, which is visible high overhead as night falls right now.

The cluster is another story, though. It has so few stars that all of them put together emit only about 60 times more light than the Sun. So it hardly compares with the Milky Way’s grandest clusters, which produce millions of times more light than the Sun.

Not only is Kim 1 faint, it faces a bleak future, because the gravitational pull of the rest of the galaxy is luring stars away from their home. One sign of this process is the cluster’s oval shape — an indication that the Milky Way’s gravity is stretching it out.

And the cluster’s outer regions are ragged — another sign that Kim 1 is in trouble. In fact, astronomers suspect that this dim cluster is disintegrating even now, and will someday vanish completely — its stars going their own separate ways as they scatter into the galaxy.


Script by Ken Croswell, Copyright 2015

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