Type

Stellar mass

Location

in the constellation Cassiopeia

Distance

2.4 million light-years (740 kiloparsecs)

Mass

23 times the mass of the Sun

Size

Diameter roughly 80 miles (140 km), about the size of Connecticut

Discovery Methods

• Detection of an accretion disk
• Measuring the motions of a companion star

IC 10 X-1

IC 10 is a little puffball of a galaxy, only a few percent the size and mass of the Milky Way. Yet its small population includes quite a few big, hot, heavy stars that are destined to blow themselves to bits as supernovae.

One such star is a companion to a star that has already done so. All that remains of the once brilliant star is its crushed core: the heaviest stellar-mass black hole yet discovered. They form a system known as IC 10 X-1 (the first cataloged X-ray source in IC 10).

Observations by space-based X-ray telescopes show that the system's X-ray energy waxes and wanes. The changing brightness indicates that the two are aligned in such a way that the bright star eclipses the black hole, which is the primary source of X-rays, once every 34.9 hours.

The alignment allows astronomers to obtain fairly precise measurements of the masses of the two objects. The black hole is about 23 times as massive as the Sun, while its bright companion is perhaps slightly heavier.

That makes IC 10 X-1 the heaviest black hole in its class — the remnants of supergiant stars. When such a star can no longer produce energy in its core, the core collapses and the star's outer layers explode. No other known stellar-mass black hole is even close to the mass of IC 10 X-1.

Astronomers suspect that the star that collapsed to form the supernova was originally about 60 times the mass of the Sun. The star contained relatively small amounts of elements heavier than hydrogen and helium. Such stars produce relatively feeble "winds" of charged particles from their surfaces, so they don't lose much material during their short lifetimes. Holding onto most of its mass allowed it to form a heavier-than-average black hole.

Before it exploded, the star was of a type known as Wolf-Rayet — the final stage of life for the heaviest class of stars, and the same class as the black hole's present-day companion.

This star is puffing some of its own material into space, forming a cloud around itself. The black hole captures some of this gas and pulls it inward, forming a small but hot ring of super-heated material known as an accretion disk. The disk produces enormous amounts of X-rays. Unlike many similar systems, in which the X-ray brightness varies by a large amount, the X-rays from IC 10 X-1 remain steady, indicating that the accretion is fed by a smooth flow of gas from the Wolf-Rayet star.

The flow won't last much longer, though. The Wolf-Rayet star is so massive that it, too, will explode as a supernova, probably leaving behind its own black hole. That will deprive the current black hole of food, so it will stop shining. After that, the two black holes will orbit each other quietly. Someday, though, if the supernova doesn't kick the two stars apart, the black holes may spiral together and merge, forming an even bigger black hole.

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This document was last modified: June 28, 2011.