The image above shows the globular star cluster known as M3. The cluster is made up of several hundred thousand stars. It is a member of our Milky Way Galaxy, located nearly 34,000 light years from our solar system.
This star cluster is located within the constellation of Canes Venatici, the hunting dogs. In 1764 the French comet hunter Charles Messier made it the third object, M3, of his now famous catalog.
M3 is thought to be about 180 light-years across, although half of the cluster's stars are located within its innermost 22 light years. M3 contains a relatively large number of "Blue Straggler" stars. These are stars that are bluer than most other stars within the cluster.
This infrared image was taken by Tom Jarrett (Infrared Processing and Analysis Center / Spitzer Science Center / Caltech) using the Palomar Observatory's 200-inch Hale Telescope with its Wide-field Infrared Camera.
UPDATE to post: Thanks to Palomar Skies reader jg for keeping me on my toes about blue straggler stars. Please note that my comments in the post as it was first worded did not reflect any of the science being done by Tom Jarrett.
jg was correct in his comments about how blue straggler stars are thought to be created. Here is a graphic from a HST press release that illustrates the leading two ideas:
Something else that I should have noted the first time around was that blue straggler stars were first discovered by astronomer Allan Sandage who was studying globular cluster M3 with the 200-inch Hale Telescope.