Stars with longest duration stellar eclipse discovered

Imagine living on a world where, every 69 years, the sun disappears in a near-total eclipse that lasts for three and a half years. That is just what happens in an unnamed binary star system nearly 10,000 light years from Earth, new research has found.

The newly discovered system, known only by its astronomical catalogue number TYC 2505-672-1, sets a new record for both the longest duration stellar eclipse (3.5 years) and the longest period between eclipses (69 years) in a binary system.

"It's the longest duration stellar eclipse and the longest orbit for an eclipsing binary ever found...by far," said the study's first author Joey Rodriguez, Vanderbilt University in Tennessee, US.

The findings were published in the Astronomical Journal.

Two unique astronomical resources made the discovery possible: observations by the American Association of Variable Star Observers (AAVSO) network and the Digital Access to a Sky Century @ Harvard (DASCH) programme.

The previous record holder for longest stellar eclipse is Epsilon Aurigae, a giant star that is eclipsed by its companion every 27 years for periods ranging from 640 to 730 days.

"Epsilon Aurigae is much closer -- about 2,200 light years from Earth -- and brighter, which has allowed astronomers to study it extensively," Rodriguez said.

TYC-2505-672-1 is so distant that the amount of data the astronomers could extract from the images was limited.

However, they were able to estimate the surface temperature of the companion star and found that it is about 2,000 degrees Celsius hotter than the surface of the sun.

Combined with the observation that it appears to be less than half the diametre of the sun it has led them to propose that it is a red giant that has had its outer layers stripped away and that this stripped material may account for the obscuring disk.

In order to produce the 69-year interval between eclipses, the astronomers calculated that they must be orbiting at an extremely large distance, about 20 astronomical units, which is approximately the distance between the Sun and Uranus.