KIC 8462852: Orphaned Exomoon Being Torn Apart May Explain Bizarre Dimming of 'Alien Megastructure' Star

An orphaned exomoon gradually being torn apart could explain the bizarre dimming behavior of a star that has puzzled scientists for years—and even made global headlines as being potential evidence of an "alien megastructure."

Astronomer's first observed Tabby's Star, otherwise known as KIC 8462852, in the 1890s. But in 2015, Tabetha Boyajian, an astrophysicist from Louisiana State University, discovered something unusual—the star's brightness would dip irregularly over a period of days or weeks.

Boyajian's observations showed that at times the star's brightness would reduce only slightly, but at other times, it fell by as much as 22 percent. Subsequent research by another team of scientists showed that the overall brightness of the star—which is located over 1,000 light years from Earth in the constellation Cygnus—was also decreasing over time.

The irregular dimming of the star—which has only been seen in a small handful of other stars—has been the subject of intense debate among scientists, who have proposed various explanations, none of which definitively explain the unusual behavior.

One of the hypotheses that was put forward states that the reductions in light are being caused by a cloud of disintegrating comets orbiting the star. Other scientists even suggested that the existence of 'alien megastructure' around the star could be responsible.

In 1960, American physicist Freeman Dyson proposed the idea that an extremely advanced—and power-hungry—alien civilization could, in theory, harness the majority of their host star's energy by building a vast structure around it to absorb its radiation.

Some have suggested that a Dyson sphere around Tabby's star could be blocking its light in an unusual way. However, this idea has been dismissed by the vast majority scientists, who say it doesn't sufficiently explain the behavior.

Now, a team of scientists from Columbia University have proposed a new explanation based on astronomical models. They say the dimming is being caused by a melting exomoon shedding dust and debris, which is then accumulating around the star.

Their findings are published in the journal Monthly Notices of the Royal Astronomical Society.

"The exomoon is like a comet of ice that is evaporating and spewing off these rocks into space," Brian Metzger, an author of the study from Columbia University, said in a statement. "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."

The exomoon—any natural satellite that orbits a body outside of our solar system—once orbited an exoplanet within the solar system. However, KIC 8462852's powerful gravitational forces essentially ripped it away, so that the moon ended up in orbit around the star.

According to the scientists, the strong radiation from the star then bombarded the moon in its vulnerable new orbit, blowing off layers of ice, dust and rock—and forming clouds that block light around the star at irregular intervals.

The teams models naturally result in the "orphaned exomoons ending up on [highly eccentric] orbits with precisely the properties previous research had shown were needed to explain the dimming of Tabby's star," Miguel Martinez, another author of the study from Columbia, said in the statement. "No other previous model was able to put all these pieces together."

If the latest results are confirmed by future studies, the researchers say it would provide evidence that exomoons are common in planetary systems throughout the universe.

"We don't really have any evidence that moons exist outside of our solar system, but a moon being thrown off into its host star can't be that uncommon," Metzger said. "This is a contribution to the broadening of our knowledge of the exotic happenings in other solar systems that we wouldn't have known 20 or 30 years ago."

While exomoons are expected to be found across the universe—a conclusion drawn from knowledge of our solar system—so far, only a handful of candidates have been identified, in large part, because they are very difficult to detect with current techniques.

Tabby's star
A new Columbia study suggests chunks of an exomoon's dusty outer layers of ice, gas, and carbonaceous rock may be accumulating in a disk surrounding Tabby's Star, blocking the star's light and making it appear to gradually fade. NASA/JPL-Caltech