From black holes to rogue radio signals, our universe is full of mysteries. A few years ago, the constellation Cygnus stole the attention of scientists with the peculiar Boyajian’s star. What made Boyajian’s star stand out from the rest was the drastic fluctuations in its brightness. It was an enigma among variable stars. That is until astronomers discovered another one just like it.
Counting Our Variables
Stars with an inconsistent apparent magnitude aren’t uncommon. Most are caused by transiting planets that partially block the star’s light, extreme sunspots on the star’s surface, or the object itself swelling and contracting. Typically, determining the cause of the shift in brightness is a relatively easy job. Observe the star for long enough and you’ll see the orbiting planet, shifting sunspots, or growth and shrinkage of the object with time.
In the Milky Way alone, astronomers have cataloged over 46,000 variable stars. Outside of our galaxy, some 10,000 more have been confirmed with at least as many other stars falling into the category of “unconfirmed variables.” These stars are grouped into intrinsic and extrinsic variables, depending on whether the source of the light modulation comes from physical changes in the body itself or external sources like eclipses.
Odd Men Out
What makes VVV-WIT-07 and KIC 8462852 so unique among variable stars is that scientists haven’t been able to figure out why they appear brighter or dimmer on any given day. One proposed reason is the presence of an uneven ring of dust around Boyajian’s star. Another possibility is abnormal convection currents beneath the star’s surface causing surges of brightness between periods of relative dimness.
More baffling than the unknown source of the fluctuations in luminosity is the degree to which Boyajian’s star varies. At one point, the star’s brightness dipped by 22%. Most variable stars only experience subtle fluctuations in their magnitude. Even weirder is the degree to which the new star, VVV-WIT-07, varies. As if dipping to three-quarters brightness wasn’t strange enough, scientists have measured magnitude variability of 80% from VVV-WIT-07, which is well beyond what any known type of transiting planet could produce.
Theories about what could be causing VVV-WIT-07’s dips in brightness range from strange to stranger. Like with Boyajian’s star, astronomers can’t rule out the possibility of an irregular orbital dust ring. Any transiting planet would have to be a Mamajek object, a sort of super-Saturn, to block that much light. Another possibility is that VVV-WIT-07 is locked in a dance with a brown dwarf, which could account for the near-blackout.
Other proposed causes are far more whimsical. The idea of an alien superstructure in orbit around Boyajian’s star and VVV-WIT-07 was put forth as a possibility. An energy-farm along the lines of a Dyson swarm could block out enough light, but such a setup would require a spacefaring alien race capable of building solar-harvesters and placing them in locked orbits around a star. As cool as that would be, it’s probably not the case. Further observations of the two stars will hopefully yield answers.