A massive star located more than 25,000 light-years from Earth became steadily dimmer over several months before returning to its normal brightness. This odd effect was most likely created by some form of the obstacle. But astronomers aren't sure what it is.
VVV-WIT-08, a red giant star, began to dim in luminosity in early 2012. The "WIT" in the star's name stands for "What Is This?" The star continued to decrease until April of that year, when it was reduced to 97 percent of its previous brilliance, rendering it almost undetectable. After that, the 100-times-larger-than-the-Sun star gradually regained its former splendor. The entire process took around 200 days from start to end.
This peculiar episode, in which VVV-WIT-08 exhibited a "smooth, eclipse-like reduction" in its regular brilliance, is detailed in a new study published late last week in Monthly Notices of the Royal Astronomical Society. The research, titled "VVV-WIT-08: the giant star that blinked," was co-led by astronomer Leigh Smith of Cambridge University's Institute of Astronomy.
Artist's impression of the binary star VVV-WIT-08
Object of the Mystery: Experts Say It's Usual For Stars to Lose Part of Their Brightness
It is now normal for stars to endure brightness dips. The most common causes are eclipsing partner stars or stars that naturally pulse. What is remarkable, though, is the length of time that a single blinking episode lasts.
There are similarities in the scientific literature, which is interesting. Every 27 years, the giant star Epsilon Aurigae undergoes a partial eclipse, dimming by around 50%. A star dubbed TYC 2505-672-1 discovered a few years ago does something similar, with an eclipse every 69 years. TYC 2505-672-1 is the longest stellar eclipse known to astronomers, lasting 3.45 years. Astronomers believe a large disc of circling dust is the most likely source in both situations.
Other stars appear to dim regularly, so this could be a thing. But, as explained in the article, the researchers are talking about a "population of long-period eclipsing binaries formed of late-type big stars and opaque-disc-hosting companions." The nature of this huge disc of opaque dust, on the other hand, is unknown.
"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," Sergey Koposov, a co-author of the study and an astronomer with the University of Edinburgh, explained in a statement released by the University of Cambridge.
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The team, which comprises astronomers from Carnegie Mellon University, University College London, and other institutions, discovered the possible long-period eclipsing binary in data collected by the European Southern Observatory's VISTA Variables in the Via Lactea Survey (VVV). The dimming was also discovered in data obtained by the University of Warsaw's Optical Gravitational Lensing Experiment (OGLE).
What Is This: Were White Dwarves And Black Holes Responsible For This Blinking Object?
"Occasionally we find variable stars that don't fit into any established category, which we call 'what-is-this?', or 'WIT' objects," Philip Lucas, co-leader of the study and a professor at the University of Hertfordshire, said per SciTechDaily. "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."
Models are created by transforming a data point into an elliptical object with uniform transparency. It's also quite thick, measuring over 37.3 million kilometers in depth, or almost a fourth of the usual distance between Earth and the Sun (AU). Scientists can't be sure of the object's entire size because of uncertainty regarding its orbit, ranging from tens of AU to hundreds of AU wide (1 AU is 150 million kilometers).
According to the report, the scientists explored a chance encounter with an unidentified passing object as a possible explanation. Still, they ruled it out since "a chance alignment with the big star demands an astonishingly huge space density of dark foreground objects." Indeed, as their simulations revealed, this idea requires an unimaginably enormous number of rogue, dark objects in the Milky Way to work. So instead, they argue that the mystery item is more likely orbitally connected to VVV-WIT-08.
A debris disc created by a white dwarf or black hole, or a disc made of stuff stripped from the star itself, are two further possibilities presented by the scientists. Although none of the explanations are particularly compelling, the scientists believe that a probable mass transfer from the big star is an "attractive" prospect.
"Despite intensive efforts, it is clear that we have left room for further work on this intriguing object!," conclude the astronomers in their study. If this population of binary objects exists, it is quite likely that the Legacy Survey of Space and Time (LSST) campaign at the future Vera Rubin Observatory will detect them. Unfortunately, the COVID-19 epidemic has caused a delay in LSST, and it is unlikely to begin until late 2023.
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