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An ancient “city” of stars passes high overhead on spring and summer evenings — a globular cluster known as the Hercules Cluster, M13. It’s a faint, fuzzy point of light in the constellation Hercules.
The cluster is about 25,000 light-years away, and it contains hundreds of thousands of stars. But they’re crammed into a region that’s only about a hundred light-years across, so the cluster contains hundreds of times more stars than are found in a similar volume of space around the Sun.
Most of the stars in globular clusters are red and faint — a strong indication that they’re among the galaxy’s oldest stars. In fact, the stars in M13 are probably at least 12 billion years old — close to three times the age of the Sun.
The stars in globulars are also different from the Sun in another way: They contain far fewer heavy elements.
The Big Bang created lots of hydrogen and helium, but almost nothing heavier than those simple elements. Everything else — from carbon and oxygen to gold and uranium — was forged in the hearts of stars. As stars die, they expel some of these elements into space, where they can be incorporated into new stars — like the Sun.
But the stars of M13 were born before most of the heavy elements found in the universe today were formed. So almost all of the heavy elements they contain are elements that the stars of M13 created on their own — elements forged over the last 12 billion years.
More about Hercules tomorrow.
Script by Damond Benningfield, Copyright 2003, 2008, 2012