star-eclipse-disk

Images from four telescopes show how a dark disk of dust passes in front of a distant star once every 27 years. ((John Monnier))

U.S. astronomers have observed a thin, dark cloud passing in front of a distant star, helping explain a mysterious eclipse first observed in the 19th century.

Epsilon Aurigae is a visible star about 2,000 light years away in the constellation Auriga, the charioteer. Since at least the 1840s, astronomers have known that something passes in front of the star every 27 years, making it appear dimmer.

Astronomers think the most likely object to cause such an eclipse would be a dim star, one so dim that its own light wouldn't be visible from Earth, being orbited by a thick disk of dust that partially obscures the light from the main star.

For the eclipse to be visible from Earth, the orbits of the dim companion star and the disk of dust around it would have to line up from our vantage point, which is a pretty unlikely arrangement.

However, the new data, combining infrared observations from four telescopes at Georgia State University, shows that this model was correct.

"This really shows that the basic paradigm was right, despite the slim probability," said John Monnier, an astronomer at the University of Michigan, in a statement.

"It kind of blows my mind that we could capture this. There's no other system like this known. On top of that, it seems to be in a rare phase of stellar life. And it happens to be so close to us. It's extremely fortuitous," he said.

Monnier's research, done with astronomers at the University of Denver and Georgia State University, appears this week in the journal Nature.

Monnier led the team that created an instrument called the Michigan Infrared Combiner that combines light from four different ground-based telescopes and amplifies the signal, making them work like a single telescope 100 times larger than the Hubble Space Telescope.