Mysterious shadow hides giant star

VVV-WIT-08 is a red giant star with 100 solar masses and 25,000 light years away from us. Ten years ago (25,010 years ago, of course) its brightness suddenly decreased drastically – down to one-thirtieth of its original value. There are indeed variable stars. In certain phases of life many types of stars show spontaneous changes. However, such a large decrease as in VVV-WIT-08 is rare. It speaks for the fact that the cause was not in the star itself, but in its environment. Did another object move in front of the star for a few hundred days and darken it?

This was the idea pursued by an international team led by Dr. Leigh Smith of the Cambridge Institute of Astronomy, who collaborated with scientists from the University of Edinburgh, the University of Hertfordshire, the University of Warsaw in Poland and the Universidad Andres Bello in Chile. Because the star is located in a dense region of the Milky Way, the researchers initially considered whether an unknown dark object might have simply drifted in front of the giant star by chance. However, simulations showed that there would have to be an implausibly large number of dark bodies floating around in the galaxy to make this scenario likely.

No, the object must be orbiting in the star system of VVV-WIT-08. The researchers calculated that it must have a diameter of at least 0.25 astronomical units (equivalent to a quarter of the distance from Earth to the Sun). Its shadow, which fell on the star from our perspective for a few hundred days, had an elliptical shape. This suggests that it could be a spherical object with a disk. However, the researchers can’t say much more yet. “It is amazing that we have just observed a dark, large and elongated object passing between us and the distant star, and we can only speculate what its origin is,” admits then co-author Dr. Sergey Koposov of the University of Edinburgh.

An international team of astronomers watched as the star VVV-WIT-08 diminished in brightness by a factor of 30, nearly disappearing from the sky. While many stars change brightness because they pulsate or are eclipsed by another star in a binary system, it is extremely rare for a star to dim and then brighten again to this extent over a period of several months. (Image: Amanda Smith, University of Cambridge)

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  • BrandonQMorris
  • Brandon Q. Morris is a physicist and space specialist. He has long been concerned with space issues, both professionally and privately and while he wanted to become an astronaut, he had to stay on Earth for a variety of reasons. He is particularly fascinated by the “what if” and through his books he aims to share compelling hard science fiction stories that could actually happen, and someday may happen. Morris is the author of several best-selling science fiction novels, including The Enceladus Series.

    Brandon is a proud member of the Science Fiction and Fantasy Writers of America and of the Mars Society.