Aliens ruled out for why Tabby’s star flickers

The first observations of Tabby’s star flickering in real time have put the last nails in the “it’s-an-alien-megastructure” coffin.

The star’s most recent winks show that the dimming is from small dust particles surrounding it, a team of more than 200 scientists and amateur astronomers reports in a paper posted at arXiv.org January 3.

The oddball star, officially named KIC 8462852, is best known for its sudden drops in brightness (SN Online: 2/2/16). Astronomers have invoked everything from evaporating comets to an enormous edifice built by intelligent aliens to explain the sporadic winks.

In March 2016, astronomer Tabetha Boyajian of Louisiana State University in Baton Rouge (for whom the star was nicknamed) and her colleagues began trying to catch light dips in the act using two automatic ground-based telescopes with the Las Cumbres Observatory, a worldwide network of telescopes.

On May 18, 2017, as Tabby’s star started to dim, at least 12 other telescopes rushed to follow up. That event turned out to be the first of four distinct light dips between May and the end of December, when the star moved behind the sun from Earth’s perspective.

Boyajian and colleagues report that the star grew dimmer in blue wavelengths than in red ones. That dimming is best explained by dust particles less than a micrometer in size, Boyajian says. If a large, opaque object — say, an alien megastructure — was blocking the star, then multiple telescopes should see the same level of dimming across many wavelengths of light. An earlier paper reported the same wavelength difference in the star’s dimming spanning several years (SN: 9/30/17, p. 11), but this is the first time it has been seen for the short-term dips.

“This is a very exciting step towards understanding this object,” says Brian Metzger of Columbia University, who was not involved in the new study. “It’s a nail in the coffin of anything where you imagine it’s some sort of solid structure.”

But declaring dust the culprit raises a new mystery. The dust is small enough that the star’s radiation should blow it away, so something must be constantly creating more of it.

“None of the ideas we have at this point are really great at putting all the pieces together,” Boyajian says. “Yeah, it’s dust, but where is it coming from? That’s still up in the air.”