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"
The Center of the Circinus Galaxy in X-Rays
16/05/2001
Are black holes the cause of X-rays that pour out from the center of the Circinus galaxy? A new high-resolution image from the orbiting Chandra X-ray Observatory has resolved the inner regions of this nearby galaxy into several smaller sources. The image is shown above in representative-color. Extended X-ray emission from the center appears to match optical light and appears consistent with a model where hot gas is escaping from a supermassive black hole at Circinus' center. At least one of the other sources varies its X-ray brightness as expected from a binary star system, indicating that the system is small yet massive, and giving credence to a model where a black hole is surrounded by doughnut-shaped ring. The region shown spans about 5000 light-years across.