APOD 1.7

For this week's APOD, I chose the picture called Globular Star Cluster, uploaded on October 9, 2010.  In the photograph, there is a bunch of stars, and there are a lot of them concentrated in the center of the picture.  There are many star clusters like this in our Milky Way Galaxy, but this one is called NGC634.  The picture was taken by Hubble's Advanced Camera For Surveys.


These types of globular star clusters are in a somewhat spherical shape because they are so gravitationally bound to do so.  And, typically, globular star clusters have older stars than those in an open cluster, and consist of huge red stars that can become hotter than the sun.  In the star cluster in the picture, there are about several hundred thousand stars.  And, this particular star cluster is estimated to be about 10 billion years old, making them older than the galactic disk.  And, because of how old star clusters are, they actually start to constrain the age of the Universe, as the Universe cannot be younger than the stars in it.   NGC634 was discovered by William Herschel in 1785, and originally cataloged it as H I.103. This star cluster is located at about 50,000 light years away from the constellation of Delphinus, which has a common name of Dolphin.  From the distance of the Hubble Camera, the star cluster spans for about 50 light years.