An accretion disk is a swirl of gas, dust and plasmaorbiting a massive celestial object, such as a star or a black hole. These materials spiral inward like a whirlpool, attracted by the central object’s gravity.
An accretion disk’s velocity increases as it draws nearer the disk’s center. Friction and gravitational forces from the central object cause the gas and dust to emit energy — lots of it. Studying that energy gives scientists clues about the object at the disk’s center. For example, accretion disks that form around black holes emit X-rays and other high-energy light. Accretion disks also form around newborn stars. These emit lower-energy infrared light.
Planets form from the dust in the disks around stars. In fact, our solar system is thought to have formed from an accretion disk that once surrounded the sun.
The largest accretion disks lie at the cores of active galaxies. About the size of our solar system, these spectacular disks whirl around supermassive black holes and flicker with high-energy light.
In telescope images, an accretion disk looks like a glowing platter. Such images can reveal the shadow of the central object if it is dark, as in the case of black holes.