A Blinking and Dimming Star May Be Caused by a Mysterious Dusty Object

The world’s most famous dimming star is KIC 8462852, better known as “Tabby’s Star” for Tabetha S. Boyajian, the astronomer whose scientific paper in 2015 revealed its peculiar propensity for dimming and glowing at irregular intervals. Speculation on causes for the dimmings ranged from dust rings to planetary debris to a second smaller binary star to an extremely large planet to the ever-popular alien-constructed Dyson sphere harvesting Tabby’s energy. While none of these conclusively explain Tabby’s dimmings, they raise the bar for other similar stars and objects to catch the attention of astronomers and the public. A candidate for 15 minutes of flame-on-flame-off fame emerged this week and it could be nicknamed ‘Dusty’ for the star-dimming cloud it’s causing, or “Wacky’ for the strange and mysterious way it operates.

“We report the discovery of a unique object of uncertain nature—but quite possibly a disintegrating asteroid or minor planet—orbiting one star of the widely separated binary TIC 400799224.”

TIC 400799224 was discovered by a team of astronomers using the Transiting Exoplanet Survey Satellite (TESS – TIC stands for TESS Input Catalog). TESS specializes in finding small exoplanets and that’s kind of what TIC 400799224 is – an exoplanet orbiting a star system around 2,300 light-years away. The Center for Astrophysics (a collaboration between the Smithsonian Astrophysical Observatory and Harvard College Observatory) reports that CfA astronomer Karen Collins and the team found the object by accident when they noticed a 25% rapid drop in brightness for a few hours, followed by several sharp jumps in brightness similar to an eclipse. (A photo can be seen here.) However, this was like no eclipse they had seen before.

“Follow-up speckle imaging determined that TIC 400799224 is actually two stars of similar brightness at 0farcs62 separation, forming a likely bound binary with projected separation of ∼300 au.”

For one thing, what they thought was a star is actually a binary system, with one star pulsating every 19.77 days. The erratic dimming is being caused by an object, probably a disintegrating exoplanet, that periodically emits clouds of dust. Beyond that, the astronomers can’t tell which star the dusty object is orbiting … a key bit of information that could explain the erratic dips in brightness.

“The cloud is also fairly optically thick, blocking up to 37% or 75% of the light from the host star, depending on the true host.”

A depiction of binary stars

According to the Center for Astrophysics, the quantity of dust emitted is quite large in relation to the size of the exoplanet – enough to cause a quick disintegration. Yet the observations show the object has not been reduced in size despite losing so much dust. That makes ‘Dusty’ unique.

“(TIC 400799224 ‘s) detailed properties differ in significant ways from the other objects listed in Table 1 and, therefore, TIC 400799224 may be in a category of its own.”

The team will continue to observe TIC 400799224 to determine what it is. Should Tabby be worried that the new dimming kid in town will take some of the spotlight astronomic spotlight away from her? Unless the astronomers think the dust is a Dyson sphere, she has nothing to worry about.

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