Star light, Star bright! Illuminating far-off galaxies at night! In the 1980s, scientists started discovering a new class of extremely bright sources of X-rays in galaxies. These Ultraluminous X-ray sources, or ULXs, are objects beaming with the light of 1 million suns, 23 million light years away. Long thought to be black holes, in the past few years Chandra X-ray Observatory data helped identify these objects as neutron stars — the cores of a massive post-supernova star. This discovery also came with clues about how these objects can shine so brightly. The latest ULX is located in the Whirlpool galaxy, also known as M51. This composite image of the Whirlpool contains X-rays from Chandra (purple) and optical data from the Hubble Space Telescope (NASAHubble) (red, green, and blue). The ULX is marked with a circle. Neutron stars are extremely dense objects — a teaspoon would weigh more than a billion tons, as much as a mountain. The intense gravity of the neutron stars pulls surroun...