The Giant Star That “Blinked”

A red big 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 top of that year it was again to its regular giant-star self.

The occasion, no matter it was, was distinctive. The star’s big, 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 available here). They suggesting {that a} disk round a companion briefly coated the star, and will achieve this once more in the future.

Blinking giant light curve
A 17-year-long lightcurve for WIT-08 exhibits that the star remained fairly constantly brilliant 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 plane as a part of the VVV survey. It displays fields dense with stars, recording their brightness time and again. Some stars keep regular, whereas others pulse in identified and common methods. But generally certainly one of them captures the eye of astronomers, who flag it as a “what is this?” star (WIT for brief).

The eighth one on this listing, cataloged as VVV-WIT-08, is a red big star that instantly started fading across the starting of 2012. While there’s a spot in observations when the star wasn’t seen, which makes it laborious to inform precisely when the fade began, the measurements that had been recorded present a easy dimming and restoration. This conduct is in distinction to the square-shape dips that happen when smaller our bodies, akin to exoplanets, cross the face of their host stars.

After ruling out the concept the star itself would possibly one way or the other be fluctuating in brightness, Smith and his colleagues estimate that no matter is obstructing the star’s gentle, it should be huge — with a radius of at the least 1 / 4 of the gap between Earth and the Sun (0.25 astronomical items), and presumably even larger. What’s extra, it appears to not be spherical, as an alternative having extra of an elliptical or egg form. In different phrases, no matter it’s, it’s positively not a planet!

Smith’s group as an alternative means that the star might have a companion, whether or not a planet or one other star, that’s itself surrounded by a disk. Such a disk may very well be each giant sufficient and of the fitting form to dam the large star’s gentle.

However, it’s nonetheless unclear what the disk can be precisely. Disks of mud and gas encompass younger stars nonetheless within the strategy of forming, however a dusty disk would block extra blue gentle than red, and the astronomers didn’t see that sample on this case. The similar goes for dusty disks round main-sequence stars. A disk round a white dwarf can be too small, and there’s no X-ray signature of the varieties 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 gas, 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 attainable 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 circumstances (maybe together with the tenth and eleventh objects on the WIT listing) during which stars dip deeply in brightness, some greater than as soon as.

The most notable of those is Epsilon Aurigae, goal of a famous observing campaign in 2009. Using interferometry, astronomers truly managed to image the disk because it crossed the face of the star again then.

While such detailed observations received’t be attainable for the far more distant WIT-08, they may nonetheless inform researchers what to search for across the blinking big and others prefer it.


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