Nesting Stars

Like a chick that’s left the nest, the Sun moves through the galaxy alone. But many of the galaxy’s stars are still in their nests — in great clusters of stars. All the stars in a cluster are members of the same brood — they were all born from the same giant cloud of gas and dust.
Two examples are near the tail of Scorpius, which is low in the south-southeast at nightfall.
The brighter one is Messier 7, to the left of the stars that mark the scorpion’s stinger. Under moderately dark skies, it’s visible to the unaided eye as a tight knot of stars. Binoculars reveal more stars, and telescopes reveal still more.
From the types of stars the cluster contains, astronomers deduce that M7 is about 200 million years old — only about five percent the age of the Sun. That youthfulness is one reason the cluster is still together. As a cluster orbits the center of the Milky Way, the combined gravity of the galaxy’s other stars and gas clouds pulls it apart. That sends its stars off on their own.
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