Alternate Names

V616 Monocerotis

Type

Stellar mass

Location

In the constellation Monoceros

Distance

2,800 to 3,400 light-years

Mass

3 to 13 times the mass of the Sun

Size

Diameter 10-45 miles (20-65 km), equal to the size of a large city

Discovery Methods

• Measuring the motions of gas
• Measuring X-rays

A0620-00

Twice in the last century, the system known as A0620-00 (for its coordinates in the sky) has flared brightly -- in 1917 and again in 1975. In the second event, an orbiting telescope detected an outburst of X-rays that was more than 100,000 times stronger than the system's normal X-ray output. That classified the system as an X-ray nova.

The outbursts may have been produced by gas suddenly funneling into a black hole. As it neared the event horizon, the gas got hotter, which made it emit more energy, including visible light and X-rays.

A0620-00 is a binary system. One member of the system is a dark, compact object that's at least three times the mass of the Sun (too heavy to be a neutron star) and probably around five times the mass of the Sun. The other is a "normal" star just one-half the Sun's mass. In most of the other known black-hole binaries, the companion star is large, massive, and bright. Astronomers aren't sure if the small companion was born along with the massive star that later formed the black hole, or if it formed from gas and dust that the massive star blew into space as a strong "wind."

The gravity of the black hole pulls at the small companion, so the star bulges toward the black hole. Because of this, as this star orbits the black hole once every 7.75 hours, we see it from different perspectives, so its brightness varies a little.

An accretion disk surrounds the black hole. As more gas is added to the disk, it may become unstable, with some of the mass dumping into the black hole and creating bright flare-ups.

At a distance of around 3,000 light-years, this may be the nearest black hole.

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This document was last modified: February 12, 2012.