Youthful Oldies

StarDate: March 4, 2010

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The stars in a cluster known as NGC 188 are all billions of years old. Most of them are faint, cool, and fairly red. But a few look like youngsters: They're bright, hot, and blue. The stars aren't young, though. Instead, they've undergone a sort of rejuvenation.

The stars are known as blue stragglers. Although they have the characteristics of youth, they can't be young because they're members of a cluster of old stars. Hot, blue stars quickly burn out and fade from sight, so there shouldn't be any left in a cluster like NGC 188. But astronomers from the University of Wisconsin, who've studied the cluster for more than a decade, have found 21 of them.

Their observations support the idea that blue stragglers have been rejuvenated. Some of the stars are members of binary systems, so they have close companions. The blue stragglers may steal gas from these companions. As the gas piles up, it gets hotter, making the stragglers look blue. A straggler may also be born when the two stars in a binary ram together and merge to make a single star, or from the merger of two stars from different binaries. These encounters bring a bit of youthful spirit back to one of the galaxy's oldest star clusters.

NGC 188 circles close around Polaris, the North Star, which stands due north throughout every night of the year. The cluster contains hundreds of stars, but it's so far and faint that you need a good-sized telescope to see it.

Script by Damond Benningfield, Copyright 2010

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