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Misleading Stars

An old star cluster has the blues. A lot of them, in fact. Astronomers have discovered dozens of blue stars in the cluster when there shouldn’t be any at all.

Messier 67 is an old cluster — roughly four billion years old. Most clusters of its type don’t stick together that long — their stars are pulled away, and the cluster simply vanishes.

As befits an old cluster, most of the stars in M67 are fairly cool, so they shine yellow or orange. But some of the stars are blue, and that’s a bit of problem. Blue stars tend to be hot and massive, so they burn out quickly. And many of them explode. So any blue stars born in M67 should have expired billions of years ago.

Today’s blue stars probably had some help in turning blue: They stole gas from companion stars. As the gas piles up on the surface of a stellar thief, it makes the surface hotter — and that makes it bluer.

Most of the “second-chance” blue stars are known as blue stragglers. But a few are called blue lurkers. They spin much faster than expected. That was discovered only recently, so the stars have been “lurking” in plain sight. They probably spin up as the gas from a companion funnels onto them — adding to the “blues” in this old star cluster.

M67 is in Cancer, the crab, and is high in the southern sky at nightfall. Through binoculars, it looks like a hazy smudge of light — the combined light of hundreds of stars that are old — even if they don’t look it.

Script by Damond Benningfield

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