July 24, 2012 | 4
The Hubble Space Telescope’s Wide Field Camera 3 took this picture of a cluster of ancient stars in the Milky Way, known as Messier 107. It is a globular cluster that is eighty light years across and about 20,000 light years from the solar system.
Globular clusters contain hundreds of thousands of stars held together in a sphere by gravity. Towards the centre of the cluster the stars are packed closer together. Globular clusters contain stars that are much older than the ones within a spiral galaxy’s arms – typically, they are the oldest in a galaxy.
Messier 107 sits in the Milky Way’s galactic halo, which surrounds its main disk, along with 150 other clusters. In dense clusters, stars can sometimes collide. But Messier 107 is not a particularly tightly packed cluster. Hubble can easily pick out individual stars, as anyone can in the photograph above.
Nobody is quite sure how globular clusters form. Many, but not all, contain stars that are all at the same stage in their evolution, suggesting that they all formed at around the same time. And globular clusters tend to be in places in the universe where stellar birth rates are high. But the details are still fuzzy, so telescopes will continue to point towards these clusters and take pictures, like the one above, to try and make clearer the universe we live in.