First Pictures: Mystery Disk Eclipses Star

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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 threeand a half suns. It appears to be about 40 percent the size of theeclipsing disk.
Other observations suggest the star has probably seen most of itshundred-million-year lifespan, having burned through its hydrogen andperhaps a good amount of its helium, noted study co-author Stencel.
In addition, Epsilon Aurigae has probably lost some of its mass, in theform of gases, to its companion's disk. But the star is still justmassive enough that it might end its life explosively, as a supernova, Stencel said. (Related: "Brightest Known Supernova Detected.")      

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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 largeeclipsing companion, on the order of a thousand times larger than thesun."
Study co-author Stencel pointed out that the actual mass of the debrisdisk is less than that of Earth, while the star inside likely has aboutsix times the sun's mass.

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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, themassive object has proved invisible at many wavelengths of light,making the disk's eclipses of Epsilon Aurigae the best chances to studythe mysterious body.
(Related: "Star 'Fireworks' Expected From Strange Eclipsing System.")

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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 Skywill help astronomers fine-tune their understanding of the EpsilonAurigae system as the star progresses through its current eclipse. Fanscan 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 cango out and see it," even without binoculars or a telescope, Stencelsaid. "Even tonight, in a clear condition, you could walk outside andlook at the star deep in eclipse."
Curious stargazers should first find the familiar constellation Orionand then scan above it in the western sky. Epsilon Aurigae is just tothe right of Capella, the top star in the constellation Auriga, theCharioteer (see star chart).