To say that the universe is a big place is an understatement. There are many galaxies containing many stars with many orbiting planets.
If you look long enough, you’re bound to encounter some interesting phenomena. How about a gas cloud big enough to make 2 million suns that boomerangs around our galaxy? Or a planet with such peculiar orbital dynamics that it creates a stellar eclipse that lasts for about 3 1/2 years once every 69 years? (And yes, that’s the proper term; “solar eclipse” only refers to our own sun.)
That bizarre eclipse is taking place in TYC 2505-672-1, a star system discovered 10,000 light-years away from Earth. Thanks to its binary star center consisting of a pair of red giant stars — one of which was stripped down to a small core but remains surrounded by a disk of material large enough to eclipse the other — this system sets a record for the longest duration stellar eclipse and the longest period between eclipses in a binary system. Astronomers estimate that to get this 69-year eclipse cycle, the two stars must orbit each other at a distance about as far as the sun is from Uranus.
This is an artist's rendition of what the pair of stars might look like:
The previous record was held by Epsilon Aurigae, a giant star located about 2,200 light-years from Earth that gets eclipsed by its companion every 27 years for periods ranging between 640 and 730 days.
You may wonder how astronomers were able to discover this phenomenon if the eclipse only happens every 69 years and lasts 3.5 years. Doesn’t this mean that most of the time you look, there’s no eclipse? And if you look during the eclipse, doesn’t it last so long that you probably won’t even notice that a star is supposed to be there?
Astronomers overcame these challenges by using thousands of photographs taken over the years. The Digital Access to a Sky Century @ Harvard (DASCH) includes images from 1890 to 1989 from a regular survey of the northern sky. By combining more than10,000 images showing the TYC 2505-672-1 star system over time, they were able to examine the long-term light curve and clearly see the stellar eclipse.
The top graph shows the light curve going back all the way to 1890, and the bottom one zooms in on just the past few years. Each dip in the lines represents an eclipse, the first one happening in the early 1940s and the second one in the early 2010s.