First Pictures: Mystery Disk Eclipses Star

Star, Pre-Eclipse

Photograph courtesy John D. Monnier, University of Michigan

Epsilon Aurigae shines at full brightness in 2008 in a picture made using the Center for High Angular Resolution Astronomy, or CHARA, telescope array on Mount Wilson in California.

Previous estimates had pegged Epsilon Aurigae at 15 times the mass of our sun. But the new CHARA data suggest the star is much smaller—more like three and a half suns. It appears to be about 40 percent the size of the eclipsing disk.

Other observations suggest the star has probably seen most of its hundred-million-year lifespan, having burned through its hydrogen and perhaps a good amount of its helium, noted study co-author Stencel.

In addition, Epsilon Aurigae has probably lost some of its mass, in the form of gases, to its companion's disk. But the star is still just massive enough that it might end its life explosively, as a supernova, Stencel said. (Related: "Brightest Known Supernova Detected.")

Published April 7, 2010

Star Eclipse Starts

Photograph courtesy John D. Monnier, University of Michigan

An enhanced picture made in November 2009 shows the mystery object starting to eclipse the star Epsilon Aurigae.

"It is clear from the early studies that [Epsilon] Aurigae is an extraordinary binary star," Edward Guinan, a Villanova University astronomer, wrote in an accompanying review also published in this week's Nature.

"Its orbital period and very long eclipse durations imply a very large eclipsing companion, on the order of a thousand times larger than the sun."

Study co-author Stencel pointed out that the actual mass of the debris disk is less than that of Earth, while the star inside likely has about six times the sun's mass.

Published April 7, 2010

Half Eclipsed

Photograph courtesy John D. Monnier, University of Michigan

An enhanced picture of Epsilon Aurigae made in December 2009 shows the dark disk eclipsing almost 50 percent of the star.

Until now, Epsilon Aurigae's companion has been elusive: By itself, the massive object has proved invisible at many wavelengths of light, making the disk's eclipses of Epsilon Aurigae the best chances to study the mysterious body.

(Related: "Star 'Fireworks' Expected From Strange Eclipsing System.")

Published April 7, 2010

Stellar Frisbee Disk

Illustration by Nico Camargo and courtesy www.citizensky.org

The dark disk eclipsing Epsilon Aurigae gets a thinner, Frisbee-like treatment in an artist's conception.

A new professional-amateur collaboration called Citizen Sky will help astronomers fine-tune their understanding of the Epsilon Aurigae system as the star progresses through its current eclipse. Fans can also follow the latest news about Epsilon Aurigae via a dedicated Twitter feed run by study co-author Stencel.

For now, "Epsilon Aurigae is still bright enough that most people can go out and see it," even without binoculars or a telescope, Stencel said. "Even tonight, in a clear condition, you could walk outside and look at the star deep in eclipse."

Curious stargazers should first find the familiar constellation Orion and then scan above it in the western sky. Epsilon Aurigae is just to the right of Capella, the top star in the constellation Auriga, the Charioteer (see star chart).

Published April 7, 2010