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Black Holes Encyclopedia

NGC 821

Printable version




in the constellation Aries

Finder Chart


100 million light-years (24.1 megaparsecs)


50 million to 100 million times the mass of the Sun


Diameter from the size of Earth's orbit to the size of Mars' orbit around the Sun

Discovery Methods


NGC 821

Astronomers discovered a likely supermassive black hole in the core of NGC 821 as part of a survey of possible host galaxies with Hubble Space Telescope. NGC 821 is classified as an elliptical galaxy, although it is slightly flattened into a disk-like shape. By measuring the orbital motions of stars near the center of the galaxy, a team of astronomers concluded that the stars are orbiting a black hole of roughly 50 million to 100 million times the mass of the Sun.

This and other black holes in the hearts of galaxies suggest that there is a link between the black hole's mass and the overall mass of the galaxy. There is also evidence that the supermassive black holes may form first, and form as a sort of gravitational "seed" to attract the gas and dust that gives birth to a galaxy's stars.



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This document was last modified: January 24, 2011.


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