M92

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Hercules, the strongman, lumbers up the eastern sky this evening. It's a large constellation that forms a sort of lopsided square. And it's home to two bright star clusters -- one famous, the other not.

Both are globular clusters -- ball-shaped clusters packed with hundreds of thousands of ancient suns. Most of the Milky Way's globular clusters formed at the same time as the galaxy itself. So examining their stars can give astronomers insight into that ancient era -- 13 billion years ago.

The famous cluster is M13. It's the brightest globular in the northern half of the sky; to the eye alone, it looks like a fuzzy little star.

But the other bright globular, M92, is also impressive -- and perhaps even more important.

M92 is notable for its extreme composition. Because globular clusters formed long ago, their stars couldn't inherit the oxygen, iron, and other heavy elements that were created by early stars and then spewed into space when the stars died. As a result, the stars in a globular consist almost entirely of the hydrogen and helium that was produced in the Big Bang.

M92 is especially pristine. While a typical globular contains a few percent as much iron as the Sun, for example, M92 has just half a percent. That makes it one of the most iron-deficient globular clusters in the entire galaxy. M92 is a stark reminder of how the ancient galaxy lacked the elements to give birth to planets like Earth -- and living beings like us.

Script by Ken Croswell, Copyright 2008

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