Dense Dwarfs

Ultra-compact dwarf galaxies are a class of very compact galaxies with very high stellar densities. An extreme example of a UCD is M60-UCD1 which contains approximately 200 million solar masses within a 160 light-year radius. The stars in its cental region are about 25 times closer together than the stars in our part of the Milky Way. M59-UCD3 is approximately the same size as M60-UCD1 with a half-light radius, but it’s 40% more luminous. This makes M59-UCD3 the densest known galaxy.

Image Credit: NASA

A Crowded Neighborhood

m60The densest galaxy in the nearby Universe may be this galaxy known as M60-UCD1. It is located near a massive elliptical galaxy 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