News & Technology

11 January 2017

‘Alien megastructure’ signal may be due to star eating a planet

WHEN you are a messy eater, it can take a long time to clean up after a meal. The slow dimming of Tabby’s star and the sudden dips in its light may be caused by orbiting debris left over from when it gobbled a planet.

The star KIC 8462852 rose to prominence in 2015, when a team of astronomers led by Yale’s Tabetha Boyajian (after whom the star is nicknamed) observed a series of abrupt dips in its brightness, in which it dimmed by up to 22 per cent before going back to normal.

There are many ideas about what causes the star’s blinking, from internal stellar dynamics to swarms of orbiting comets to an enormous alien megastructure.

Things got more complicated in January 2016, when a review of old photographic plates revealed that Tabby’s star dimmed by 14 per cent between 1890 and 1989. It faded by another 3 per cent over the four years it was observed by the Kepler space observatory.


Now Brian Metzger at Columbia University in New York and his colleagues have a theory that could explain both the brief dips in light and the gradual dimming. The group thinks Tabby’s star is just returning to its natural state – after a messy meal.

If Tabby’s star devoured a planet in the past, the planet’s energy would have made the star temporarily brighten, then gradually dim to its original state. Depending on the size of the planet, this event could have happened anywhere between 200 and 10,000 years ago.

As the planet fell into its star, it could have been ripped apart or had its moons stripped away, leaving debris orbiting the star in eccentric orbits. Every time the debris passes between us and the star, it would block some light, making it seem as if the star is blinking (

“Consuming a planet could explain the star’s brief dips in light and its gradual dimming”

Next time we see the light from Tabby’s star dip, Metzger hopes that astronomers will glimpse the signatures of that debris.

A collision like this explains the behaviour of Tabby’s star well, says Jason Wright at Penn State University in University Park. “This paper puts a merger scenario on the table in a credible way.”

This article appeared in print under the headline “Strobe-light star could have eaten a planet”