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    Superfast Mystery Foreign Objects From Smaller Galaxy Are Invading the Milky Way

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    Rare hypervelocity stars, otherwise known as stars that have been ejected at a high velocity from the center of the galaxy after interaction with a black hole, are tearing through the Milky Way galaxy. According to research presented at the National Astronomy meeting in Hull, UK, they are runaway stars.

    The hypervelocity stars are traveling at a speed of 300-700 kilometers per second, which is faster than our galaxy's escape velocity.

    There have only been 20 confirmed cases so far, but most of them are B-type stars, which means they are larger than the Sun.

    ​There has been huge debate around the origin of these breakaway stars. Some scientists believed that some might have come from the Milky Way's rotational center, whereas others believe that they could be foreign objects which have come into our solar system. 

    A paper published in the Monthly Notices of the Royal Astronomical Society in April 2017 makes the argument that all the hypervelocity stars are foreign objects.

    According to the research, the idea is that these super-fast stars were part of a binary system, and that have escaped their original home, otherwise known as the Magellanic Cloud (LMC), which is a neighboring satellite galaxy.

    Scientists at the University of Cambridge looked at the data from the Sloan Digital Sky Survey to build computer simulations of runaway stars escaping from the LMC to the Milky Way.

    They predicted that there are approximately 10,000 runaway stars spread across the sky.

    "Earlier explanations for the origin of hypervelocity stars did not satisfy me," said Douglas Boubert, lead author of the paper and a PhD student at the University of Cambridge Institute of Astronomy.

    "The hypervelocity stars are mostly found in the Leo and Sextans constellations — we wondered why that is the case," he added.

    ​The closer the stars are on the binary system, the faster they orbit one another, and then they can reach speeds fast enough to become hypervelocity stars.

    According to researchers, runaway stars that start out in the Milky Way are too slow to become hypervelocity stars because the blue B-type stars are not able to orbit close enough to their companion star in the binary system.

    However, fast moving galaxies like the LMC could give rise to quick stars, so the fastest ones will be able to escape the galaxy's pull.

    "These stars have just jumped from an express train — no wonder they're fast. This also explains their position in the sky, because the fastest runaways are ejected along the orbit of the LMC towards the constellations of Leo and Sextans," said Rob Izzard, co‑author of the paper and a Rutherford fellow at the University of Cambridge Institute of Astronomy.

    "We'll know soon enough whether we're right. The European Space Agency's Gaia satellite will report data on billions of stars next year, and there should be a trail of hypervelocity stars across the sky between the Leo and Sextans constellations in the North and the LMC in the South," he added.

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    Tags:
    galaxies, space objects, stars, astronomy, space exploration, space, Institute of Astronomy, Royal Astronomical Society, University of Cambridge, European Space Agency (ESA), Milky Way, United Kingdom
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