Close Companions

StarDate: May 20, 2013

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For a star, companionship isn’t always a good thing. A star in the constellation Ophiuchus, for example, has been whittled away by a domineering companion — a black hole. Only a fraction of the star remains.

An artist's concept shows the small star (left) dumping gas onto the accretion disk around the black hole [ESA]MAXI J1659 systemThe system is known as MAXI J1659. It was discovered three years ago when it produced a brilliant outburst. Observations by X-ray telescopes in space showed that the system likely consists of two objects — a black hole about three times as massive as the Sun, and a small companion star. The two stars are so close together that the black hole steals some of the companion’s gas. Before the gas enters the black hole, it forms a hot disk around the black hole. Sometimes, so much gas flows into the disk that it causes an eruption like the one seen in 2010.

Models of stellar evolution suggest the companion star originally was a little heavier than the Sun. The star that gave birth to the black hole was even heavier, but it quickly used up its nuclear fuel. Billions of years ago, its core collapsed to form a black hole, while its outer layers exploded.

Since then, the black hole has stripped away most of the companion’s outer layers, leaving a faint remnant that’s only about one-fifth as massive as the Sun.

The two bodies are probably about a half-million miles apart, and they orbit each other once every 2.4 hours. At that rate, the companion star whips around the black hole at more than a million miles per hour.

 

Script by Damond Benningfield, Copyright 2013

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