Scientists Say: Accretion Disk

These whorls of glowing space dust swirl around the most massive bodies of the cosmos

This black hole is surrounded by an accretion disk of superheated dust, gas and plasma (illustrated).


Accretion disk, (noun, “Uh-kree-shun disk”)

An accretion disk is a swirl of gas, dust and plasma orbiting 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.

In a sentence

Images taken with radio telescopes show the vibrant accretion disk surging around the black hole at the heart of our own galaxy.

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Katie Grace Carpenter is a science writer and curriculum developer, with degrees in biology and biogeochemistry. She also writes science fiction and creates science videos. Katie lives in the U.S. but also spends time in Sweden with her husband, who’s a chef.

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