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 apparently has. Other calculations show that dust might be involved, but that still isn't known for sure yet (other data suggested something denser or even solid) and that 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."
The latest dip of Boyajian's Star
It also seemed at first that the dip had ended after a day or two at most, but now it seems it may be continuing after all. As mentioned by Jason Wright on Twitter very early yesterday morning:
"Yes! Latest photometry shows this event is complex and continuing. thanks!"
Whether the current dip(s) will get any deeper this time is still unknown, but we will see. The good thing about this one is that a lot of instruments are now pointing at Boyajian's Star, watching the event as it happens. Before, there was only the Kepler data to go by from the earlier dips, and possible evidence of much longer-term gradual dimming of the star over centuries from older photographic plates. This in itself has become a topic of much debate.
Some of the previous dips also occurred in small clusters, so it will also be interesting to see if that happens again this time around.
Whatever the explanation turns out to be, it will be fascinating. A previously unknown bizarre but natural pheneomena, or, just perhaps, something even more exotic.
The original discovery details can be found on the "Where's the Flux?" website and you can also follow the detailed active discussions on the formal Reddit forum. All the Twitter updates, many now, are posted there as well. More information as it becomes available.