Why does this star have such a cumbersome name? The Kepler Input Catalog (or KIC) is a publicly searchable database of roughly 13.2 million stars targeted by the Kepler Space Probe, which is attempting to find planets in orbits around those stars (thus far, the probe has found more than 3000 planets). When Kepler finds a possible planet, that star then receives a new designation as a KOI (a Kepler Object of Interest).
KIC 8462852 has not been given a KOI number, despite how interesting it has become. But it has gotten a nickname: Tabby’s Star, which is much easier to remember. It is an F-type main sequence star. If you have a five inch or larger telescope, you can see it in the Constellation Cygnus roughly halfway between the bright stars Deneb and Delta Cygni. It has a magnitude of about 12 so it would be invisible to your naked eye. F-type stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K. Tabby’s Star’s surface temperature is about 6750 K. Our Sun, in contrast, is a G-type star with a surface temperature of about 5772 K). F-type stars are yellow-white in color, like our Sun.
The reason that Tabby’s Star has become an object of note to astronomers is due to the discovery of very odd light fluctuations, specifically frequent, non-periodic dips in brightness, along with two large recorded drops in luminosity that seem to happen every 750 days. What would cause these light fluctuations? According to astronomers, the most likely explanation is that many small masses are orbiting KIC 8462852 in a tight formation.
The changes in luminosity are significant. The first big dip on March 5, 2011 was 15 percent. The second, on February 28, 2013 decreased the star’s brightness by 22 percent. Astronomers have calculated that a planet the size of Jupiter would cause a light dip of only about 1 percent, so what in the world could be causing such large blockages of the light from Tabby’s Star?
As if that were not enough spookiness for this star, a study of about a hundred-year’s-worth of old photographic plates suggests that the star dimmed by about 20 percent between 1890 and 1989. Not all researchers have been convinced by this research, but in the last month, a study of the light measured by the Kepler Space Telescope over the last four years shows the star dimming by about 0.34 percent per year—and then by 2.5 percent during one 200-day period before returning to its original rate of fading.
Out of the 150,000 stars being monitored by the Kepler space probe, it is the only one that behaves this way. In fact, out of all the stars ever observed by astronomers, none have ever acted like this.
The scientist whose name has been given as a nickname to this star speculated in her 2015 paper that first described this star’s oddness. One of the first things that she and her colleagues considered was the possibility that it was all just data artifacts—errors in how the data was collected, transmitted, or recorded. However, they were able to eliminate that as a possible explanation. One possibility that she emphasized in her paper was that the star might just have an unusually large number of comets around it. Or, it might be a series of giant gas giant planets with very large ring structures of a sort that would put Saturn to shame. Another suggestion was that it could just be interstellar dust, or maybe an asteroid field of some sort. Others suggested that the star might be younger than first thought, and thus have material still coalescing around it on its way to become future planets. However, a spectroscopic study of the system using the NASA Infrared Telescope Facility found no evidence for any coalescing material around the star.
Another suggestion was that perhaps a couple of large planets around the star recently collided. However, the Nordic Optical Telescope in Spain did a search for the dust that such a huge collision would have created. Such warm dust would glow in the infrared. However, once again, there was no observed excess infrared energy, thus ruling out massive planetary collision debris being responsible for the observed dimming of Tabby’s Star. Other observations by NASA’s Spitzer Space Telescope and the Wide-field Infrared Survey explorer have likewise ruled out any of the proposed explanations for the weirdness being witnessed with this star.
Unsurprisingly, therefore, some, such as Astronomer Jason Wright, have raised the possibility that the observations might be due to artificial objects that are part of a megastructure, such as a Dyson Swarm. In 1960 the mathematician Freeman Dyson theorized that technological civilizations would have ever increasing energy needs, needs that might lead them to decide to attempt to capture their star’s solar energy by building a system of orbiting structures designed to collect it: think solar panels of enormous dimensions engulfing a star.
Further studies of KIC 8462852 are in the works. Tabetha Boyajian, the author of the original paper on the star, has raised more than 100,000 dollars through a Kickstarter fund raiser. It’s enough money to fund a year’s use of the Las Cumbres Observatory Global Telescope Network to continue observation of the star in additional wavelengths in order to reveal new details on the composition of the objects blocking the star’s light.
All the researchers agree that the likelihood of extraterrestrial intelligence being the cause of the dimming is very low. However, it has become a focus of SETI research since natural explanations have yet to fully explain the dimming phenomenon. In October 2015, the SETI Institute used the Allen Telescope Array to look for radio emissions from possible intelligent extraterrestrial life in the vicinity of the star, but found nothing. Researchers have also gone back and looked at old archival VERITAS gamma ray observatory observations from 2009 through 2015 looking for pulsed optical beacons, also to no avail.
Most likely whatever is going on with KIC 8462852 is entirely natural. But no one knows for sure just yet.