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Black Holes Encyclopedia

M82 X-1

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Intermediate mass


In the constellation Ursa Major

Finder Chart


11 million light-years (3.4 megaparsecs)


Approximately 1,000 times the mass of the Sun


Diameter equal to the size of Mars

Discovery Methods


M82 X-1

Something near the core of the galaxy M82 is pumping out copious amounts of X-rays. But the source, cataloged as M82 X-1, isn't steady. One possible explanation is a black hole perhaps 1,000 times as massive as the Sun.

The X-ray source is in or near a cluster of hot, young stars about 600 light-years from the core of M82, which is classified as a starburst galaxy. The galaxy is giving birth to tens of thousands of stars, versus only a handful in the Milky Way.

Using space-based X-ray telescopes, astronomers have seen the source of X-rays grow periodically stronger and fainter. The type of X-rays, and the way they rise and fall, are similar to the X-rays produced by accretion disks around black holes in the Milky Way that are a few times the mass of the Sun.

But the rise and fall of the X-rays in M82 X-1 takes longer than those of the known black holes in the Milky Way. That suggests that the source of the X-rays is larger; it takes more time for light (and other forms of electromagnetic energy, including X-rays) to cross a larger object than a smaller one, so any "flickering" is slower.

From the length of the variations, and the distance to M82, astronomers calculate that the most likely source for the X-rays is a black hole that is roughly 1,000 times as massive as the Sun. The black hole is pulling in gas from a large, heavy companion star. As the gas approaches the black hole it's heated to millions of degrees, so it emits X-rays.

If the black hole is confirmed, M82 X-1 would become one of just a handful of known intermediate-mass black holes.

Follow-up observations by a sensitive network of radio telescopes, however, detected no radio waves from M82 X-1, suggesting that if the source is a black hole, it must be less massive than indicated by the X-ray observations.

So while there is a strong case for the intermediate-mass black hole, it's not a conclusive one. More observations are needed to confirm the source of the X-rays from M82 X-1.


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This document was last modified: March 14, 2012.


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