An analogy is to consider the human population in a large school complex offering classes from kindergarten to 12th grade, where even a brief study would be sufficent for a trained scientist to fully characterize the development of the human species from early childhood through to adulthood. This week's image presents NGC 2099, also known as Messier 37, a rich open cluster located about 5000 light years away, in the constellation Auriga. The cluster, containing about 2000 stars, was imaged with the CFH12K mosaic camera in October 1999. It is a member of a carefully selected sample of open clusters, spanning a range of ages from about 1 to 5 billion years old. This sample was selected so that the Astronomers could study the white dwarf population.
White dwarfs are the most common kind of star in the Galaxy.
All stars whose initial mass is up to about 5 times that of the sun will end up as white dwarfs once the nuclear energy stores are depleted. It is the fate of the sun. However, many chapters the white dwarf story remain to be written, mainly because these earth-sized, very dense balls of carbon and oxygen are exceedingly faint and therefore difficult to study. Since the members of an open cluster are all at the same distance, they will define very tight sequences in a color-magnitude diagram. The diagram for NGC 2099 can be viewed here .