There’s something strange near the galactic center.
Some 25,000 light-years from Earth, astronomers have found a weird star that almost blinked out of existence for several months before reappearing.
Astronomers believe the star, named VVV-WIT-08, could belong to a new class of star – giant beasts over 100 times the Sun that are eclipsed by a mysterious orbiting body once every few decades.
Stars with peculiar dimming signatures are an endless fascination. Although space is mostly relatively empty, it stands to reason that, with all the stuff out there, some of it will line up in such a way that stars are dimmed from our terrestrial perspective from time to time.
It’s not always easy to tell what that stuff is, though. A giant planet? Space dust? Debris from a disrupted object? A cosmic dragon?
The case of VVV-WIT-08 is a doozy. Although other stars have exhibited similar dips in light, none have been so deep. The culprit, astronomers think, could be another star or planet, surrounded by a thick, opaque disk of dust on a long orbit around VVV-WIT-08, that covers the star completely when it passes in front of our view.
“It’s amazing that we just observed a dark, large and elongated object pass between us and the distant star and we can only speculate what its origin is,” said astronomer Sergey Koposov from the University of Edinburgh in Scotland.
The model of an orbital companion with a giant disk isn’t without precedent. One famous, well-known example is Epsilon Aurigae, a supergiant star and with a disk-shrouded companion on a 27-year orbit that dims the star by about 50 percent for up to 730 days.
Then there’s the system TYC 2505-672-1, a red giant star with a dusty companion on a 69-year orbit that eclipses the star for a period of 3.5 years.
The survey that picked up VVV-WIT-08 (the “WIT” stands for “what is this?” because astronomers are great like that), the VISTA Variables in the Via Lactea (VVV) survey, picked up a couple of other candidates that seemed to exhibit the same behavior. Because the data on those stars aren’t as complete as the data for VVV-WIT-08, they are yet to be described.
We know the star’s peculiarity isn’t an error, though. The dimming was also observed by the Optical Gravitational Lensing Experiment using the Warsaw Telescope in Chile, which means it wasn’t a glitch (although it would have to be a very strange sort of glitch).
The data show that the dimming event lasted for approximately 200 days, with a nearly symmetrical light curve, quenching the star’s light by up to 97 percent. The density of objects required in that region of space for the chance alignment of two random bodies is much higher than observed, so the team believes the two objects are gravitationally bound.
The orbital period is unknown, but it has to be at least a few decades, according to mathematical modelling.
And the discovery suggests such systems may not be all that uncommon.
“There are certainly more to be found, but the challenge now is in figuring out what the hidden companions are, and how they came to be surrounded by discs, despite orbiting so far from the giant star,” said astronomer Leigh Smith of the University of Cambridge.
“In doing so, we might learn something new about how these kinds of systems evolve.”
The research has been published in the Monthly Notices of the Royal Astronomical Society.