Black Hole
A black hole is an astronomical object whose gravity is so strong that nothing—even light—can escape from within its event horizon. It forms when a massive star’s core collapses or through other processes, and may have an accretion disk of infalling matter that emits radiation. Supermassive black holes at galaxy centers influence stellar orbits, and mergers produce gravitational waves.
Source: nasa.gov
APODs including "Black Hole"
Chandra Deep Field
12/10/2002
Officially the Chandra Deep Field - South, this picture represents the deepest ever x-ray image of the Universe. One million seconds of accumulated exposure time with the orbiting Chandra X-ray Observatory went in to its making. Concentrating on a single, otherwise unremarkable patch of sky in the constellation Fornax, this x-ray image corresponds to the visible light Hubble Deep Field - South released in 1998. Chandra's view, color coded with low energies in red, medium in green, and high-energy x-rays in blue, shows many faint sources of relatively high-energy x-rays. These are likely active galaxies feeding supermassive central black holes and large clusters of galaxies at distances of up to 12 billion light-years. The stunning picture supports astronomers' ideas of a youthful universe in which massive black holes were much more dominant than at present.