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[Music]

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[Music]

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Using archival data from NASA's decommissioned

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RXTE X-ray satellite, researchers have discovered a rare

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type of black hole lurking in M82, a galaxy about 

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12 million light-years away. Known as M82 X-1,

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the object is the galaxy's brightest X-ray source.

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It was long suspected of being an exceptional midsize black hole, too big to

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be made by a dying star, yet much smaller than the monsters found in the hearts of

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galaxies, but definitive evidence had never materialized.

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Now, through careful analysis of RXTE data, astronomers have

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shown that M82 X-1 weighs in at about 400 times the mass of

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our sun. Measured masses for black holes formed by stars reach

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about 25 solar masses, and those found in galaxy centers weigh at least

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10,000 times more. Only a handful of black holes have been

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discovered with inferred masses between these extremes. Astronomers

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measured M82 X-1 by finding a special signature in its X-ray glow.

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Hot gas orbiting a black hole emits X-rays.

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Near the bring of the black hole, various physical effects create hot spots, which

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produce variations as they orbit. These signals encode

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important clues to the black hole's mass. One important signal comes

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in the form of stable pairs with a 3-to-2 relationship, meaning that one

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flashes three times for every two flashes of the other. In

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searching through six years of RXTE observations of M82 X-1,

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astronomers recently found this key signature. One hot spot

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flashes 5.1 times a second, while the other flickers 3.3 times a second--

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a solid 3-to-2 relationship. These

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signals, combined with other previously variations, pointed to an accurate

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mass of about 400 suns. With that finding,

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M82 X-1 now joins the exclusive club of middle-mass

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black holes. [Music]

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[Beeping]

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[Beeping]