As more data comes in, it's seeming less and less likely to be a massive alien construction project circleor – at one point right after its discovery in 2015 – the star. But the latest hypothesis to explain the mysterious phenomenon is still pretty weird: a melting moon.
A new study published in the Royal Astronomical Society's Monthly Notices suggests the overall dimming is caused by the accumulation of debris from just such an exomoon (the term for any moon beyond our solar system) around Boyajian's Star.
"The exomoon is like a comet of ice that is evaporating and spewing off these rocks into space," said Brian Metzger, a Columbia University astrophysics professor and lead author on the study. "Eventually the exomoon will completely evaporate, but it will take millions of years for the moon to be melted and consumed by the star. We're so lucky to see this evaporation event happen."
While aliens or swarms of comets were Among some early explanations for the star's odd behavior, more scientists are beginning to agree that it's probably.
Metzger and colleagues' theory goes like this: At some point there was a planet with a moon orbiting Boyajian's star, but something destroyed the planet and the star snatched up the exomoon and placed it in a new orbit around the star itself. This exposes the former to intense new levels of radiation that are slowly melting and ripping it apart. The accumulation of fine bits and larger chunks of debris could explain both the long and short-term dimming behaviors.
What's also interesting about the idea is that while there are promising candidates that we think could be exomoons, the existence of moons beyond our solar system has not yet been confirmed.
"But a moon being thrown off into its host star can't be that uncommon," Metzger said.
Perhaps. Although we've never directly observed that happen before. One thing we have seen, though, is an intelligent civilization that has begun to circle the celestial body it occupies with all kinds of artificial satellites and debris.
I'm not betting aliens are the real explanation, but I'm just saying …