A purple large star almost disappeared from the sky for about 200 days in 2012. At its minimal that April, solely 3% of its gentle was arriving at Earth. Then it slowly brightened once more till by the tip of that yr it was again to its regular large-star self.
The occasion, no matter it was, was distinctive. The star’s large, easy dip in brightness solely occurred as soon as over the course of the 17 years that two surveys, the VISTA Variables within the Via-Lactea (VVV) and Optical Gravitational Lensing Experiment (OGLE), have been monitoring that portion of the sky.
Leigh Smith (University of Cambridge, UK) and colleagues will report the “blinking” star within the Monthly Notices of the Royal Astronomical Society (preprint out there right here). They suggesting {that a} disk round a companion briefly coated the star, and will achieve this once more someday.
A 17-year-lengthy lightcurve for WIT-08 reveals that the star remained fairly persistently vivid apart from an enormous, easy, and symmetric dip that lasted about 200 days in 2012.L. Smith et al. / Monthly Notices of the Royal Astronomical Society 2021“What Is This?”
For years, the VISTA telescope on the La Paranal Observatory in Chile has been systematically protecting a area of the sky alongside the middle of the Milky Way and alongside a part of the galactic aircraft as a part of the VVV survey. It screens fields dense with stars, recording their brightness time and again. Some stars keep regular, whereas others pulse in identified and common methods. But typically one among them captures the eye of astronomers, who flag it as a “what is this?” star (WIT for brief).
The eighth one on this checklist, cataloged as VVV-WIT-08, is a purple large star that all of the sudden started fading across the starting of 2012. While there’s a niche in observations when the star wasn’t seen, which makes it exhausting to inform precisely when the fade began, the measurements that had been recorded present a easy dimming and restoration. This habits is in distinction to the sq.-form dips that happen when smaller our bodies, reminiscent of exoplanets, cross the face of their host stars.
After ruling out the concept that the star itself would possibly in some way be fluctuating in brightness, Smith and his colleagues estimate that no matter is obstructing the star’s gentle, it have to be huge — with a radius of at the very least 1 / 4 of the space between Earth and the Sun (0.25 astronomical items), and presumably even larger. What’s extra, it appears to not be spherical, as a substitute having extra of an elliptical or egg form. In different phrases, no matter it’s, it’s undoubtedly not a planet!
Smith’s staff as a substitute means that the star may have a companion, whether or not a planet or one other star, that’s itself surrounded by a disk. Such a disk might be each giant sufficient and of the proper form to dam the enormous star’s gentle.
However, it’s nonetheless unclear what the disk could be precisely. Disks of mud and fuel encompass younger stars nonetheless within the technique of forming, however a dusty disk would block extra blue gentle than purple, and the astronomers didn’t see that sample on this case. The identical goes for dusty disks round principal-sequence stars. A disk round a white dwarf could be too small, and there’s no X-ray signature of the forms of disks round neutron stars or black holes.
One risk is {that a} planet in shut orbit across the star stripped away a few of its fuel, surrounding itself in a gaseous cocoon. But even this doesn’t clarify all of the observations. As the researchers conclude, “Despite intensive efforts, it is clear that we have room left for further work on this intriguing object!”
Blinking Giants Abound
Meanwhile, it’s doable that WIT-08 could be a member of a small however increasing group of stars with disk-enshrouded companions. The group consists of a number of different instances (maybe together with the 10th and 11th objects on the WIT checklist) by which stars dip deeply in brightness, some greater than as soon as.
The most notable of those is Epsilon Aurigae, goal of a well-known observing marketing campaign in 2009. Using interferometry, astronomers really managed to picture the disk because it crossed the face of the star again then.
While such detailed observations gained’t be doable for the rather more distant WIT-08, they might nonetheless inform researchers what to search for across the blinking large and others prefer it.
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