A crowded but ancient "œcity" of stars passes high overhead this evening. It's a globular cluster known as M13. It looks like a faint, fuzzy point of light in the constellation Hercules.
M13 is about 25,000 light-years away, and it contains hundreds of thousands of stars. They're crammed into a region that's only about a hundred light-years across, so there are 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 fairly red and faint -- a strong indication that they're among the oldest stars in the entire galaxy. In fact, the stars in M13 are probably a good 12 billion years old or more -- almost three times the age of our Sun.
The stars in M13 and most other globulars differ 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.
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 were created by M13's own stars -- elements forged over the last 12 billion years.
We'll talk about another cluster in Hercules tomorrow.
Script by Damond Benningfield, Copyright 2003, 2008
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