ESO/L. Calçada

Talk about a long-distance relationship. A pair of stars have the longest and most infrequent eclipses ever seen – and one star may be devouring the other.

When a pair of stars orbit each other so that one star periodically blocks the light of its partner from our viewpoint on Earth they are dubbed eclipsing binaries. The prototype is Algol, or “the ghoul” in Arabic, and medieval astrologers considered it the most dangerous star in the sky. Even with the naked eye, you can see one of the Algol pair fade every few nights as its partner passes in front of it.

Until now, the binary with the longest gap between eclipses was Epsilon Aurigae. It is also visible with the naked eye, but its eclipses occur only once every 27.1 years.


Extreme version

Now Joseph Rodriguez of Vanderbilt University in Nashville, Tennessee, and his colleagues have found an eclipsing binary named TYC 2505-672-1, in the constellation Leo Minor, with a record-breaking period of 69.1 years. “It’s really an extreme version” of Epsilon Aurigae, he says.

By combining 120 years of historical data with contemporary data from ongoing surveys, Rodriguez and his colleagues showed that the main star, a red giant, faded once during the second world war and again from 2011 to 2014. The eclipses lasted a remarkable 3.45 years – also a new record.

The other object is a small white star embedded in a huge opaque disc, which is responsible for the lengthy eclipse. The white star used to be a red giant, too, but Rodriguez says the gravity of its companion star may be tugging away material to create the disc.

Too far apart

Ed Guinan of Villanova University in Pennsylvania prefers a less violent scenario. “The stars are too far apart for one star to strip away material from the other,” he says. They are separated by roughly the same distance as the sun and Uranus.

Instead, Guinan thinks the opaque disc may be the result of the former red giant shedding its outer layer – eventually becoming a planetary nebula like the Ring nebula.

The next eclipse should tell us more but that won’t occur until 2080. But Rodriguez, now 27, hopes to live long enough to see it.

Journal reference: Astronomical Journal, in press, arxiv.org/abs/1601.00135