Observing a gigantic blinking star near the centre of the Milky Way

Astronomers have observed a huge ‘blinking’ star near the centre of the Milky Way, more than 25,000 light-years away.

An international group of astronomers spotted the star – VVV-WIT-08 – close to the Milky Way’s centre, diminishing in brightness by a factor of 30, to the point it almost disappeared from the sky.

While many stars shift in brightness as they pulsate or are eclipsed by another star in a binary system, it is incredibly unusual for a star to become dimmer over a period of several months and then illuminate again.

The team have theorised that VVV-WIT-08 may be part of a new class of ‘blinking giant’ binary star system, where a giant star 100 times bigger than the Sun is eclipsed once every few decades by a currently unobserved orbital companion. The companion, which could be another star or a planet, is encircled by an opaque disc, which covers the giant star, resulting in its disappearance, then reappearance in the sky.

The study is published in Monthly Notices of the Royal Astronomical Society.

The discovery was led by Dr Leigh Smith from Cambridge’s Institute of Astronomy, in collaboration with researchers at the University of Edinburgh, the University of Hertfordshire, the University of Warsaw and Universidad Andres Bello.

“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,” commented co-author Dr Sergey Koposov from the University of Edinburgh.

As the star is situated in a dense region of the Milky Way, the scientists contemplated whether an unknown dark object could have coincidentally drifted in front of the giant star. However, simulations indicated that there would have to be an improbably great quantity of dark bodies floating around the Galaxy for this scenario to be truly plausible.

One other star system of this sort has been recognised for a long time. The giant star Epsilon Aurigae is partly eclipsed by a huge disc of dust every 27 years but only dims by around 50%. Another example – TYC 2505-672-1 – was discovered a few years ago and retains the current record for the eclipsing binary star system with the longest orbital period of 69 years, a record for which VVV-WIT-08 is currently a contender.

The researchers have also discovered two more of these peculiar giant stars in addition to VVV-WIT-08, indicating that these could be a new class of ‘blinking giant’ stars for astronomers to examine.

“Occasionally, we find variable stars that don’t fit into any established category, which we call ‘what-is-this?’, or ‘WIT’ objects. 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,” added project co-leader Professor Philip Lucas of the University of Hertfordshire.

It appears that there are approximately sic known star systems of this type, comprised of giant stars and large opaque discs. “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,” concluded Smith. “In doing so, we might learn something new about how these kinds of systems evolve.”

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