A giant star called VVV-WIT-08 exhibited a smooth, eclipse-like drop in brightness to a depth of 97% in 2012; minimum brightness occurred in April 2012 and the total event duration was a few hundred days, according to an analysis of data from the VISTA Variables in the Via Lactea survey (VVV), a project using the British-built VISTA telescope in Chile and operated by ESO.
An artist’s impression of the VVV-WIT-08 binary system. Image credit: Amanda Smith, University of Cambridge.
VVV-WIT-08 is a giant star located more than 25,000 light-years away in the constellation of Sagittarius.
It may belong to a new class of ‘blinking’ binary system, where a giant star — 100 times larger than the Sun — is eclipsed once every few decades by an as-yet unseen orbital companion.
The companion, which may be another star or a planet, is surrounded by an opaque disk, which covers the giant star, causing it to disappear and reappear in the sky.
“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 Dr. Sergey Koposov, an astronomer at the University of Edinburgh.
Since the star is located in a dense region of the Milky Way, Dr. Koposov and colleagues considered whether some unknown object could have simply drifted in front of VVV-WIT-08 by chance.
However, simulations showed that there would have to be an implausibly large number of dark bodies floating around the Galaxy for this scenario to be likely.
One other star system of this sort has been known for a long time. The giant star Epsilon Aurigae is partly eclipsed by a huge disk of dust every 27 years, but only dims by about 50%.
A second example, TYC 2505-672-1, was found a few years ago, and holds the current record for the eclipsing binary star system with the longest orbital period — 69 years — a record for which VVV-WIT-08 is currently a contender.
“Occasionally we find variable stars that don’t fit into any established category,” said VVV project co-leader Professor Philip Lucas, an astronomer at the University of Hertfordshire.
“We really don’t know how these blinking giants came to be. It’s exciting to see such discoveries from VVV after so many years planning and gathering the data.”
“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 disks, despite orbiting so far from the giant star,” said Dr. Leigh Smith, an astronomer in the Institute of Astronomy at the University of Cambridge.
“In doing so, we might learn something new about how these kinds of systems evolve.”
The study was published in the Monthly Notices of the Royal Astronomical Society.
Leigh C. Smith et al. 2021. VVV-WIT-08: the giant star that blinked. MNRAS 505 (2): 1992-2008; doi: 10.1093/mnras/stab1211