Astronomers have spotted a giant star “blinking” 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, whose luminosity decreased by a factor of 30 so that it almost disappeared from the sky. While many stars change in brightness because they pulsate or are eclipsed by another star in a binary system, it is exceptionally rare for a star to weaken over a period of several months and then light up again.
Researchers believe that VVV-WIT-08 may belong to a new class of “flashing giant” binary star system, where a giant star – 100 times larger than the Sun – is eclipsed once every few decades by a companion invisible orbital. The companion, which can be another star or a planet, is surrounded by an opaque disc, which covers the giant star, causing it to disappear and reappear in the sky. The study is published in Monthly notices from the Royal Astronomical Society.
The discovery was led by Dr Leigh Smith of the Cambridge Institute of Astronomy, working with scientists from the University of Edinburgh, the University of Hertfordshire, the University of Warsaw in Poland and Andres Bello University in Chile.
“It is amazing that we have just observed a dark, tall and elongated object pass between us and the distant star and we can only speculate on its origin,” said co-author Dr Sergey Koposov of the ‘University of Edinburgh.
Given that the star is located in a dense region of the Milky Way, the researchers wondered if an unknown dark object could have simply drifted past the giant star by chance. However, simulations have shown that there would have to be an implausibly high number of dark bodies floating around the Galaxy for this scenario to be likely.
Another such star system has been known for a long time. The giant star Epsilon Aurigae is partly eclipsed by a huge disk of dust every 27 years, but only darkens by about 50%. A second example, TYC 2505-672-1, was found a few years ago and holds the current record for the eclipse binary star system with the longest orbital period – 69 years – a record for which VVV-WIT -08 is currently a contender.
The UK-based team also found two more of these particular giant stars in addition to VVV-WIT-08, suggesting that it could be a new class of ‘flashing giant’ stars that astronomers must study.
VVV-WIT-08 was found by the VISTA variables in the Via Lactea Survey (VVV), a project using the UK-built VISTA telescope in Chile and operated by the European Southern Observatory, which has observed the same billion stars for almost a decade to research examples with varying brightness in the infrared part of the spectrum.
Project co-leader Professor Philip Lucas of the University of Hertfordshire said: ‘Every now and then we find variable stars that do not fit into any established category, which we call’ what is what is it? I don’t know how these flashing giants came into being. It’s exciting to see such discoveries from VVV after so many years of planning and gathering the data. “
While VVV-WIT-08 was discovered using VVV data, the darkening of the star was also observed by the Optical Gravitational Lensing Experiment (OGLE), a long-term observation campaign conducted by the University of Warsaw. OGLE makes observations more frequently, but closer to the visible part of the spectrum. These frequent observations were essential for the modeling of VVV-WIT-08, and they showed that the giant star faded by the same amount in visible and infrared light.
There now appear to be about half a dozen known potentials for star systems of this type, containing giant stars and large opaque disks. âThere is certainly more to be found, but the challenge now is to determine what the hidden companions are and how they were surrounded by discs, despite their orbit so far from the giant star,â Smith said. “In doing so, we could learn something new about how these types of systems evolve.”