O Christmas Tree, O Christmas Tree,
How lovely are your branches!

That’s certainly true for the branches of the Christmas Tree star cluster – a family of young stars in the constellation Monoceros, the unicorn. The cluster’s brighter stars form the outline of a Christmas tree. Other stars look like ribbons of lights decorating the tree.

The cluster is about 2500 light-years away. All of its stars are infants – no more than a few million years old.

The most impressive member of the cluster is 15 Monocerotis. It’s a binary – two stars bound by their mutual gravitational pull. One of the stars appears to be about 10 times the mass of the Sun, while the other is more than 30 times the Sun’s mass.

Both stars are tens of thousands of degrees hotter than the Sun. Such stars produce a lot of ultraviolet energy. The U-V zaps giant plumes of hydrogen gas that permeate the cluster, making the gas shine bright pink – forming the branches of the Christmas Tree. Blobs of cold gas and dust create dark silhouettes against that background. New stars are taking shape inside some of those blobs.

The Christmas Tree Cluster climbs into view in the east in early evening. Under dark skies it’s just visible to the eye as a faint smudge of light. A telescope reveals a few of its individual stars and the faint glow of the gas. Long-exposure images reveal the full beauty of this cosmic Christmas tree.

Script by Damond Benningfield