The fastest-moving stars that zip through the Milky Way galaxy are likely fugitives from another galaxy, findings of a new study have revealed.
Hypervelocity Stars
Although scientists suspect that the Milky Way hosts about 10,000 of these galactic objects known as hypervelocity stars, only about 20 of these stars have been directly observed in our galaxy.
Based on computer simulations using data from the Sloan Digital Sky Survey, scientists said they suspect these speeding stars were originally from a small satellite galaxy called Large Magellanic Cloud. Each of these stars was also once the other half of a binary star system, wherein two stars orbit one another.
Galactic Fugitives
Researchers said that explosive breakups likely sent these stars speeding so fast that they escaped their home galaxy's gravitational pull and wandered into the Milky Way.
"These stars have just jumped from an express train — no wonder they're fast," said Rob Izzard, from the Institute of Astronomy, who is part of the study published in the Monthly Notices of the Royal Astronomical Society.
"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."
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With mass equivalent to that of 4 million suns, scientists said these hypervelocity stars, which travel at several hundred kilometers per second, govern the orbit of the stars in the vicinity.
Scientists also think these objects are important in the study of the overall structure of the Milky Way as they have zipped through the large expanse of our galaxy.
"These are stars that have traveled great distances through the Galaxy but can be traced back to its core — an area so dense and obscured by interstellar gas and dust that it is normally very difficult to observe — so they yield crucial information about the gravitational field of the Milky Way from the center to its outskirts," said Elena Maria Rossi, from Leiden University in the Netherlands.
Rossi is part of a team that discovered six new hypervelocity stars using the artificial brain of the European Space Agency's Gaia satellite.
Researchers also think studying how these stars travel may unveil the secrets of dark matter and the supermassive black hole that lies at the center of our galaxy. Although the dark matter halo is not visible, its gravity acts on stars, and scientists can gain insights from a star's trajectory and velocity that are influenced by gravity from different parts of the Milky Way.
"If you're looking at a herd of cows, and one starts going 60 mph, that's telling you something important," Ben Bromley, from University of Utah, said after the discovery of a bright hypervelocity star in 2014. "You may not know at first what that is. But for hypervelocity stars, one of their mysteries is where they come from — and the massive black hole in our galaxy is implicated."
