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Copy of current version of the article in my user space for later use off wiki to make a Science20 article. Article is a collaboration by myself and @Darkfrog24: as the main editors.

The Tabby's taking a scheduled dip and not to kill fleas. On the night of May 18 into 19, a robotic 14-inch Celestron telescope at Farborn Observatory in Arizona watched Tabby's star lose brightness by a dramatic 3% and counting, confirming a prediction that the star would undergo its unusual dimming events once every 750 days. Other major telescope projects and citizen astronomers have confirmed these findings. The dip was complex and continued through to Sunday, after a brief rise in brightness over the weekend. It seems to have ended now, with tweets from Jason Wright reminding us that the dips came in clumps before and from Tabby Boyajian saying "will we have a flurry of dips to come? Stay tuned!"

Tabby's star, also called Boyajian's Star and officially designated KIC 8462852, came to attention during the Kepler telescope project, which continuously monitored more than 150,000 stars simultaneously, from May 2009 to May 2013, with the primary goal of detecting exoplanets. If a star grows dimmer but then recovers, a planet may have passed in front of it. But Tabby's star is showing something else. An exoplanet can cause its sun to dim by perhaps 1% and not for very long. Some of Tabby's dips have been this mild, but others have hit 20% and lasted weeks. It also tends to recover only partially, slowly showing a net dimming over the years.

	Tabby's star… went through a lot of very strange dimming events that got up to 22% dimmer during the Kepler Mission, and since then we've been eagerly awaiting another dip. And the reason that we've been waiting for that is that whatever is causing the star to get dimmer will leave a spectral fingerprint behind.
—Jason Wright of Penn State

"Tabby's star… went through a lot of very strange dimming events that got up to 22% dimmer during the Kepler Mission, and since then we've been eagerly awaiting another dip. And the reason that we've been waiting for that is that whatever is causing the star to get dimmer will leave a spectral fingerprint behind," said Jason Wright of Pennsylvania State University. "So if it's a lot of dust between us and the star that's passing by, it should block more blue light than red light. If there's gas in that dust, that gas should absorb very specific wavelengths. So we’ve been eager to see one of these changes, these dips in the star, so we can take the spectra." He also addressed space fans via Twitter: "ALERT:@tsboyajian's star is dipping This is not a drill. Astro tweeps on telescopes in the next 48 hours: spectra please!"

Tabby's star has become a favorite among space fans and both professional and citizen astronomers, with a plethora of ideas about what might be causing its behavior. A comet's tail of dust and gas can spread over a region as large as a star or larger. It could be that pesky space dust or stellar indigestion after chowing down on a planet. Some have even hypothesized that alien civilizations might be harvesting the sun's energy using a Dyson sphere mid-construction, a Dyson swarm, or similar apparatus.

In 1960, physicist Freeman Dyson first suggested searching space for evidence of a spherical structure completely enclosing a star. He suggested that an advanced civilization, a few centuries ahead of us technologically, could make it out of asteroids, comets, or large planets such as Jupiter. They could use it, he hypothesized, to harness all the solar power from their host star which they would convert to waste heat as part of their civilization's energy metabolism. However, this would create excess infrared radiation, which astronomers have not observed for Tabby's star. Fans of the Dyson sphere or swarm model for Tabby's star think that it could be used for some other purpose, like beaming signals to other stars, or that the structures might lie within a disk seen edge on, so that most of the infrared is radiated away from the direction of observation from Earth. Search for Extraterrestrial Intelligence (SETI) devoted six nights of observation time to Tabby's star in the fall of 2016 as part of the Breakthrough Listen project. No radio or laser pulse signals have been detected yet.

Tabby's star had its first major dip 800 days into the Kepler observations and a series of further large dips lasting for a few months each started 1500 days in. Astronomers predicted Thursday's dip by hypothesizing that it was caused by material orbiting Tabby's star with an orbital period of around 750 days. However, no substantial dip was noticed during the first 800 days. One idea is that whatever blocks out the star actually formed during that brief interval of time. Possibly, two planetary embryos collided after Kepler started its observations of the Tabby's star system. Many such collisions have taken place in Earth's solar system, including the theorized collision that formed the Moon. However to give Kepler even a decent chance of spotting such a rare event, there would have to be an average of 10,000 such collisions per system.

It is also possible that the dips are associated with the orbiting remnants of a planet eaten by the star 10,000 years ago. Astronomers now believe that such events are quite common, with the example of Wasp 12 eating a Jupiter sized planet right now. However, they estimated that unless we were exceptionally lucky again, ten Jupiters' worth of planets and other debris would need to fall into an average star in its lifetime to explain these observations. This would make them very common. Jason Wright commented, "This paper puts the merger scenario on the table in a credible way, I think this moves it into the top tier of explanations"

At the time of its discovery by Tabetha Bayajian, Tabby's star was the only star known to have such huge dips in its light. Another one was discovered in 2016, EPIC 204278916, a young star, leading the authors to suspect a warped inner disk or transiting comets. Tabby's star is an F-type main-sequence star slightly larger and brighter than our sun, while EPIC 204278916 is a young pre-main sequence star on its way towards becoming an M type red dwarf rather smaller and dimmer than our sun.

The next step is to examine the dimming events with instruments able to spread out the light into a spectrum. If an object, natural or otherwise, is blocking Tabby's light, it will change its color slightly, and leave a fingerprint of some sort in the stars spectrum, such as darker lines at particular frequencies or a dip in the spectrum over a range of frequencies.

The follow on observations after the Kepler project were funded by a $100,000 kickstarter to continuously monitor Tabby's star. Other organizations monitoring this current Tabby's star dimming event include the University of Tennessee, Arizona's MMT Observatory, Mauna Kea's W.M. Keck Observatory, Las Cumbres Observatory Global Telescope Network, and the American Association of Variable Star Observers.. Tabby's star was originally discovered by volunteers for the Planet Hunters citizen science project, which was implemented to search for planet transits in the Kepler data using the unique pattern finding capabilities of the human eye. This buzz of discussion is what alerted the professional astronomers to it.

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Sources

Monica Young. "Finally! The Galaxy’s Most Mysterious Star Is Dipping" — Sky and Telescope, May 19, 2017

K.N. Smith. "SETI Tunes Into Tabby’s Star with Radio Telescopes" — Astronomy.com, October 31, 2016

Matt Williams, Universe Today. "Finally, an explanation for the "alien megastructure?"" — Phys Org, January 12, 2017

Minor Sources

Tabetha Boyajian. "Tweet: will we have a flurry of dips to come? Stay tuned!" — Twitter, May 21, 2017
Jason Wright. "Tweet: Latest photometry from last night; this event seems to have ended, but remember than in Q16 they came in clumps." — Twitter, May 21, 2017

Tabetha Boyajian (Louisiana State), Steve Croft (UC Berkeley), Jason Wright (Penn State), Andrew Siemion (UC Berkeley), Matthew Muterspaugh (Tennessee State), Michael Siegel (Penn State), Bruce Gary (amateur), Shelley Wright (UCSD), Jerome Maire (UCSD), Andres Duenas (UCSD), Clayton Hultgren (UCSD), JonJohn Ramos (UCSD). "A Drop in Optical Flux from Boyajian's Star" — Astronomer's Telegram, May 21, 2017