Star system with longest-lasting stellar eclipse discovered

Scientists have discovered a new star system where every 69 years the bigger star disappears in a near-total eclipse that lasts for three and a half years, setting a record for the longest duration stellar eclipse and the longest period between eclipses in a binary system.

The newly-discovered system, known only by its astronomical catalogue number TYC 2505-672-1, is a binary star system nearly 10,000 light years from the Earth.
The next eclipse in the system will occur in the year 2080, researchers said.

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

The previous record holder 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," said Rodriguez.

The leading explanation is that Epsilon Aurigae consists of a yellow giant star orbited by a normal star slightly bigger than the sun embedded in a thick disk of dust and gas oriented nearly edge on when viewed from the Earth.

"One of the great challenges in astronomy is that some of the most important phenomena occur on astronomical timescales, yet astronomers are generally limited to much shorter human timescales," said co-author Keivan Stassun, professor at Vanderbilt.

"Here we have a rare opportunity to study a phenomenon that plays out over many decades and provides a window into the types of environments around stars that could represent planetary building blocks at the very end of a star system's life," said Stassun.

The new system is similar to the one at Epsilon Aurigae, with some important differences, researchers said.

It appears to consist of a pair of red giant stars, one of which has been stripped down to a relatively small core and surrounded by an extremely large disk of material that produces the extended eclipse.

"About the only way to get these really long eclipse times is with an extended disk of opaque material. Nothing else is big enough to block out a star for months at a time," 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.

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

The study was published in the Astronomical Journal.