NASA's Hubble and Chandra Find Evidence for Densest Nearby Galaxy
Chandra X-ray Center said:
The galaxy, known as M60-UCD1, is a type of “ultra-compact dwarf galaxy”. It was discovered with NASA’s Hubble Space Telescope and follow-up observations were done with NASA’s Chandra X-ray Observatory and ground-based optical telescopes.
Observations from the W. M. Keck Observatory on the summit of Mauna Kea, Hawaii, characterized it as the most luminous known galaxy of its type and one of the most massive, weighing 200 million times more than our Sun.