Type

Stellar mass

Location

In the galaxy NGC 300, in the constellation Sculptor

Distance

6 million light-years (1.85 megaparsecs)

Mass

15 times the mass of the Sun

Size

Diameter about 45 miles (75 km) roughly equal to the size of a large county

Discovery Methods

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

NGC 300 X-1

NGC 300 X-1 is the most-distant stellar-mass black hole yet detected. It is about six million light-years away in NGC 300, a spiral galaxy that is a member of the Sculptor group of galaxies.

The discovery was made possible by the great girth of the black hole and the brilliance of its companion star.

The companion is a Wolf-Rayet star, which appears to be about 26 times as massive as the Sun, and about 10,000 times brighter.

The two stars orbit each other once every 32 hours. At such close range, the companion dumps large amounts of gas onto the black hole. The material forms a bright accretion disk, which is so hot that it produces copious amounts of X-rays. In fact, the system was discovered by an orbiting X-ray telescope and first studied in detail by a second X-ray satellite.

A detailed study with the Very Large Telescope in Chile measured the geometry of the system, which allowed astronomers to calculate the masses of both stars. The study suggests that the black hole is about 15 times as massive as the Sun, making it one of the heaviest stellar-mass black holes yet discovered.

The Wolf-Rayet star is nearing the end of its life, so it is undergoing a series of rapid changes in its core. In a million years or so, its outer layers will explode and its core will collapse to form another black hole.

The blast may rip the system apart, pushing the exploding star away from the current black hole at high speeds -- perhaps high enough for the star to escape NGC 300. If the two black holes remain bound to each other, though, in a few billion years they will merge to form a single black hole.

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This document was last modified: March 29, 2011.