Bizarre Boyajian’s Star (‘alien megastructure’ star) is dipping again!

Artist’s concept of Boyajian’s Star with a huge swarm of comets. Image Credit: NASA/JPL-Caltech

The weird star called Boyajian’s Star (aka Tabby’s Star or KIC 8462852) has been fascinating astronomers and people in general because of its weird behaviour of experiencing sudden, unusual dips in brightness which all current theories have so far had difficulty explaining. Now, the star has started dipping again after a long period of “normal” activity.

The dips, first seen by the Kepler Space Telescope in 2015, have been as much as several percent of the star’s brightness, up to about 22%. For Boyajian’s Star, even an object the size of Jupiter would only cause a decrease in brightness of less than one percent at most. Theories have ranged from huge groups of comets to clouds of dust or gas, something intrinsic to the star itself, or even “alien megastructures” such as a Dyson Sphere or a Dyson Swarm. Whatever the explanation, it is not a commonly known phenomenon, such as other well-understood “dipping stars” which are much younger than Boyajian’s Star and still have their planetary debris disks from when they formed. Boyajian’s Star shouldn’t have one anymore, and no other studies have indicated there is one. Some of the dips, such as day 792 (of Kepler observations), also seem to have a nice, regular shape to them which is interesting.

In the past couple days, starting on May 19, the star finally starting dipping again, about 3% so far, which is what astronomers have been patiently waiting for, not knowing if it ever would again. Several ground-based telescopes have been busy analyzing the spectra from the star, which Kepler couldn’t do, which should help to narrow down theories. The new results are very early so far, but may support the idea of something periodically orbiting the star about every 750 days or so. Only further study can verify that however. Astronomer Tabetha Boyajian herself, whose initial research inspired the continuing investigation, had predicted, based on previous dips, that the star might dip again in May 2017 if it was something orbiting the star. And indeed it has. Other calculations show that dust might be involved, but that still isn’t known yet (other data suggested something denser or even solid) and the “object/objects” might be about five times the radius of the Sun in overall size. As noted by David Kipping on Twitter:

“Back of the envelope: if period ~750d, circular orbit & events last 2.5d, transiting objects are ~5 times the radius of the Sun.”

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