Astronomers have seen a giant ‘flashing’ star towards the center of the Milky Way, more than 25,000 light-years away.
An international team of astronomers observed the star, VVV-WIT-08, decreasing in brightness by a factor of 30, so that it almost disappeared from the sky. While many stars change in brightness because they pulsate or are darkened by another star in a binary system, it is unusually rare for a star to fade over a period of several months and then light up again.
The researchers believe that VVV-WIT-08 may belong to a new class of “flashing giant” binary star systems, in which a giant star that is 100 times larger than the sun is obscured 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 that covers the giant star and causes it to disappear and reappear in the sky. The study is published in Monthly announcements from the Royal Astronomical Society.
The discovery was led by Dr. Leigh Smith of the Cambridge Institute of Astronomy, who worked with researchers at the University of Edinburgh, the University of Hertfordshire, the University of Warsaw in Poland, and the Universidad Andres Bello in Chile.
“It’s amazing that we’ve just seen a dark, large and elongated object pass between us and the distant star, and we can only wonder what its origin is,” said co-author Dr. Sergey Koposov from the University of Edinburgh.
Since the star is located in a dense area of the Milky Way, the researchers considered whether an unknown dark object could simply have drifted in front of the giant star. However, simulations showed that there would have to be an improbably large number of dark bodies floating around the galaxy for this scenario to be probable.
Another star system of this kind has been known for a long time. The giant star Epsilon Aurigae is partially eclipsed by a huge dust disk every 27 years, but is only attenuated by approx. 50%. Another example, TYC 2505-672-1, was found a few years ago and holds the current record for the darkening binary star system with the longest orbital period – 69 years – a record that VVV-WIT-08 is currently challenging.
The British-based team has also found two more of these peculiar giant stars in addition to VVV-WIT-08, suggesting that these may be a new class of “flashing giant stars” that astronomers can examine.
VVV-WIT-08 was found by the VISTA variables in the Via Lactea study (VVV), a project using the British-built VISTA telescope in Chile and operated by the European Southern Observatory, which has observed the same one billion stars for almost a decade to search for examples of varying brightness in the infrared part of the spectrum.
Project Counsel Professor Philip Lucas of the University of Hertfordshire said: “Occasionally we find variable stars that do not fit into any established category that we call ‘what is this?’ Or ‘WIT’ objects. We really do not know how these flashing giants came to be. It is exciting to see such discoveries from VVV after so many years of planning and collecting data. “
While VVV-WIT-08 was detected using VVV data, the attenuation of the star was also observed by the Optical Gravitational Lensing Experiment (OGLE), a long-running observation campaign run by the University of Warsaw. OGLE makes more frequent observations, but closer to the visible part of the spectrum. These frequent observations were the key to modeling VVV-WIT-08, and they showed that the giant star dimmed by the same amount in both visible and infrared light.
There now appear to be about half a dozen potential known star systems of this type, containing giant stars and large opaque disks. “There is certainly more to find, but the challenge now is to find out what the hidden companions are and how they came to be surrounded by disks, despite orbiting so far from the giant star,” Smith said. . “That way, we might learn something new about how these kinds of systems evolve.”
Blowing stars in the universe: Rare insight into the evolution of stars
Monthly announcements from the Royal Astronomical Society (2021). DOI: 10.1093 / mnras / stab1211
Provided by the University of Cambridge
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