The densest galaxy in the nearby Universe may be this galaxy known as M60-UCD1. It is located near a massive elliptical galaxy NGC 4649, also called M60, about 54 million light years from Earth. Packed with an extraordinary number of stars, M60-UCD1 is an “ultra-compact dwarf galaxy”. It was discovered with the Hubble Space Telescope and follow-up observations were done with the Chandra X-ray Observatory and ground-based optical telescopes. It is the most luminous known galaxy of its type and one of the most massive, weighing 200 million times more than our Sun.

This composite image shows the region near M60. Data from the Chandra X-ray Observatory are pink and data from the Hubble Space Telescope are red, green and blue. The Chandra image shows hot gas and double stars containing black holes and neutron stars and the Hubble image reveals stars in M60 at the right edge of the frame.

Image Credit: NASA