Second 'dimmer switch' star spotted

'Tabby's Star' gets a friend and it's even stranger, but let's not do the 'alien megastructure' thing again okay?

Broken, but still good: Kepler keeps turning in the science

One curious case of “what's that?” in astronomy is a puzzle: two gets astrophysicists on the way to an answer. An oddly-dimming star called EPIC 204278916 (EPIC in this article) might help boffins understand the “Dyson sphere” (no, it's not) Tabby's star.

The group led by Simone Scaringi from the Max Planck Institute for Extraterrestrial Physics has published their observations of EPIC at Arxiv, here.

Looking at data from the Kepler K2 mission, the researchers found that over nearly 79 days of observations, EPIC showed “irregular dimmings” of up to 65 per cent, for around 25 days in the observation period.

That's got the aliens-built-a-Dyson-sphere-to-harvest-all-their-sun's-energy crowd excited again, because even Tabby's star (KIC 8462852) doesn't dip anything like as far – its dimming only lops 22 per cent off the light we receive from it.

The Max Planck group says it's probably a gas disk with the right orientation, or a cloud of comets, that's getting between EPIC and Earth: “With the assumption that the transiting object(s) are in circular orbits we can place tight constraints on the orbital parameters in a plane defined by the semi-major axis (a) and the transiting clump radius (Rc).”

As well as the K2 observations taken in 2014, there have been follow-ups carried out at the Atacama Large Millimeter/submillimeter Array (ALMA) show “clear evidence of a resolved tilted disk”.

It's also possible, the study notes, that we're seeing early-stage planets: EPIC itself is a “pre-main sequence” star less than 11 million years old, around the same size as the sun, but with only half the mass.

That makes it a nice candidate for watching the early business of planet formation:

“EPIC 204278916 could constitute the first system where a planetesimal-sized body has been witnessed to be tidally disrupted by the parent star upon a close encounter. This would be then a direct evidence of the presence of km-sized bodies in a protoplanetary disk, a crucial step towards planet formation”, the study notes.

The researchers want to keep watching EPIC, because if there are large objects diving close enough to suffer tidal effects, they could break up in just a few orbits. ®

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