This Hubble Space Telescope image shows the central portion of the M15 globular cluster in ultraviolet light. Surprisingly, the center of M15 contains many very hot blue stars (15 are shown in this image). Generally, only young stars are blue. But globular clusters like M15 are extremely old. So why are there blue stars at the center of this cluster? Astronomers believe they exist because of the crowded conditions. This image is only 2 light years across, less than the distance from Earth to Proxima Centauri, the nearest star to our Sun, yet look how many stars crowd this small space (most of the blue stars are in the imageΓÇÖs central half light year). Current theory suggests that the stars are so close to each other that they have
