Astronomers think the object shown in this Chandra X-ray Observatory image (in box) may be an elusive intermediate-mass black hole. Located about 32 million light-years from Earth in the Messier 74 galaxy (M74), this object emits periodic bursts of x-rays at a rate that suggests it is much larger than a stellar-mass black hole but significantly smaller than the supermassive black holes found at the centers of galaxies. Few such middling black holes have been discovered, and scientists aren't sure how they form.

Photograph courtesy NASA/CXC/U. of Michigan/J. Liu et al./ NOAO/AURA/NSF/T. Boroson