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21 Feb 2020 18:57
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  •   Home > News > International

    Vampire white dwarf star feeding on neighbour spotted in Kepler data

    A newly discovered "vampire system" offers a glimpse of what could befall our solar system in a few billion years, say astronomers.


    A newly discovered "vampire system" offers a glimpse of what could befall our solar system in a few billion years, say astronomers.

    They uncovered the cosmic feeding frenzy while trawling through data from the now-defunct Kepler Space Telescope.

    The astronomers found a white dwarf star — the dense remains of an old star — feasting on an object known as a brown dwarf in a system 3,000 light years away in the constellation of Scorpius.

    They say the discovery, published in the journal Monthly Notices of the Royal Astronomy Society, provides new insights into periodic outbursts known as dwarf novas.

    Capturing such an event is tricky, said study co-author Brad Tucker of the Australian National University.

    "These outbursts happen so quickly," Dr Tucker said.

    "That's why this unique ability to harness Kepler has allowed us to see it and spy on it in a way that hasn't really been done before."

    What's a dwarf nova?

    Dwarf novas are created when the gravity of a white dwarf star sucks the hydrogen off a brown dwarf.

    "A brown dwarf is kind of like a big Jupiter," Dr Tucker explained.

    "We joke that it's a failed star, but it's really something that's bigger than Jupiter but not quite as big as another star."

    Hydrogen sucked off the companion builds up around the white dwarf until it reaches a critical level.

    The same process happens in some types of supernovas, but instead of a brown dwarf the neighbour is much bigger.

    "If that brown dwarf was bigger and was just another star [the white dwarf] would eventually explode as a type 1a supernova," Dr Tucker said.

    Instead, he said, only the disc of material surrounding the white dwarf explodes in flashes, a bit like a car spluttering.

    Ultimately, the white dwarf will suck the life out of its brown dwarf neighbour if it is close enough.

    "It's in some ways a better analogy of a vampire than [a supernova].

    "A supernova will steal some hydrogen and explode, where these will take it all."

    We don't know what will happen to the brown dwarf in this system, but the outlook is grim.

    The two objects are very close — a distance equivalent from Earth to the Moon — and orbit each other every 82 minutes.

    A similar scenario could play out in our own solar system billions of years in the future.

    "Our Sun will turn into a white dwarf," Dr Tucker said.

    "Our white dwarf will eventually, if it is close enough, feed off Jupiter."

    How to hunt down a vampire

    About 100 dwarf nova have been found so far in a sky full of billions of stars.

    "We think white dwarf stars are common, but they are really hard to find because they are small," Dr Tucker said.

    "Its hard to get a picture of them without seeing them do something like this."

    Using specially designed software developed by Ryan Ridden-Harper, now at the Space Telescope Science Institute, the team were able to track the 30-day feeding frenzy from beginning to end.

    "With the precise data from the Kepler Space Telescope we could study the first hours of the super-outburst," Dr Ridden-Harper.

    "Surprisingly, we found the system begins to brighten very slowly for the first 10 hours, before rapidly brightening by 1,600 times."

    At the peak of the outburst temperatures reached up to 11,700 degrees Celsius — a phenomenon that hadn't been previously predicted by models.

    The astronomers will now use the software to comb through more data from Kepler and its replacement TESS, the Transiting Exoplanet Survey Satellite for similar events.

    "We know about the big things like supernova decently well," Dr Tucker said.

    "But we do not have a good handle on [smaller fainter things at the ends of their lives] because we've never been able to look at these things on such short time scales."

    The power of space surveys

    Astronomer Jonti Horner of the University of Southern Queensland said the discovery is a testament to the power of large survey telescopes such as Kepler and TESS.

    "This gives you a whole new window on the Universe where you can dig through all these databases and find things that are just waiting to be discovered," said Dr Horner, whose own team recently found two new exoplanets in TESS data.

    While Dr Horner is not convinced our Sun will come close enough to Jupiter to become a dwarf nova, he said the latest discovery highlighted the diversity of stars.

    "Binary systems are interesting, they are peculiar, and they are not what you could imagine."

    Around 40 to 50 per cent of what you see in the night sky are multiple-star systems.

    "[Dwarf nova] are not hugely rare, but they are not all that common either because you need a binary star system that is close enough.

    "This is just another of those discoveries that reminds us that everything in the night sky is more complicated."

    © 2020 ABC Australian Broadcasting Corporation. All rights reserved


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