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Starts With A Bang

It’s dimming! Astronomers jump at opportunity to solve the mystery of Tabby’s star

An illustration of a storm of comets around a star near our own, called Eta Corvi. The comet scenario is one explanation for the dimming around Tabby’s star, one that a high-quality astronomical spectrum should be able to validate or rule out. Image credit: NASA / JPL-Caltech.

The oddest star known in the galaxy is dimming again, and this time it might give up some of its secrets!

“As far as I can tell, every telescope that can look at it right now is looking at it right now.” –Matt Muterspaugh

Of all the 150,000+ stars imaged by NASA’s Kepler, the most bizarre has to be KIC 8462852: Tabby’s Star.

Kepler was designed to look for planetary transits, where a large planet orbiting a star could block a tiny fraction of its light, reducing its brightness by ‘up to’ 1%. Tabby’s star has brightness dips that put that 1% figure to shame. Image credit: Matt of the Zooniverse/Planet Hunters team.

While other stars show small, periodic dips in their brightness due to transiting planets, Tabby’s star shows something unique.

Different steps in the Kepler time series data that show the periodic and aperiodic dimming of KIC 8462852, with incredibly large brightness changes. Image credit: Tabby Boyajian and her team of PlanetHunters.

Its dips are much larger in magnitude by up to a factor of 20, and show up irregularly in time.

A dusty debris disk either around the star itself or the planets that orbit it close in would emit infrared radiation, where none is seen. Image credit: ESA, NASA, and L. Calcada (ESO for STScI).

The only known stars that show such flux dips are very young, with protoplanetary disks surrounding them.

The lack of infrared excesses near the star highly disfavor a protoplanetary disk around KIC 8462852. An outer disk is still a possibility, but the orbital period would be all wrong for these large flux dips. Image credit: Infrared: IPAC/NASA (2MASS), at left; Ultraviolet: STScI (GALEX), at right.

Infrared and ultraviolet observations rule out a protoplanetary disk here; astronomers must consider other explanations.

Artist’s conception of the extrasolar ring system circling the young giant planet or brown dwarf J1407b. Worlds with extraordinary ringed systems could produce large flux dips, but those dips would be periodic in nature. Image credit: Ron Miller.

Perhaps a series of collisions, dusty planets, or extraordinary ringed structures blocks the starlight, but those signals should be periodic.

Originally, a scenario of a shattered comet was considered to explain Tabby’s star. Instead, a series of long-period comet-like objects with massive dust halos could cause these temporary, transient flux dips. Image credit: NASA/JPL-Caltech.

Perhaps a massive set of disintegrating comets bombards the system, causing an irregular series of dimming events.

The red lines (models) and the green lines (data) can be matched very well from a massive object-with-a-dust cloud model with very few free parameters, but it will take detailed follow-up observations to confirm this picture. Image credit: L. Neslusan and J. Budaj, via

But other observations showed that Tabby’s star has dimmed by 20% since 1900, something neither proposal explained.

The Harvard light curve of star KIC 8462852, along with two other stars whose flux hasn’t changed. Image credit: Bradley E. Schaefer, via

Perhaps, as many suggested, this was evidence of an alien megastructure being constructed?

The idea of enshrouding a star entirely in light-gathering material is known as a Dyson sphere. While under construction, it could block more and more of the light from the star. Image credit: public domain art by CapnHack.

But another astrophysical scenario could explain it: a recently devoured planet.

An artist’s impression of HD 189733 b, a Hot Jupiter so close to its host that its atmosphere is being boiled off into space. Over time, it will be devoured entirely, something that may have happened to Tabby’s star not so long ago. Image credit: NASA / GSFC.

Gases would dim the star overall, while outbursts and flares create irregular flux dips.

A solar flare from our Sun, which is far lower in magnitude and light-blocking capabilities than needed to explain Tabby’s star. But a devoured planet could cause the outbursts needed. Image credit: NASA’s Solar Dynamics Observatory / GSFC.

A quality light spectrum, taken during the ongoing dimming, could finally discern which model is correct.

The flux from Tabby’s star over time, as shown on May 21, 2017 during the latest flux dip event. Via Twitter at Image credit: Las Cumbres Observatory / Tabitha Boyajian.

Mostly Mute Monday tells the story of an astronomical object, image or phenomenon in visuals, pictures and no more than 200 words.

Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.


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