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Deep-space drifters

According to researchers at the Smithsonian Astrophysical Observatory in Massachusetts, several stars were discovered that were ejected from the galactic center at millions of miles per hour.

The first stellar "exile" found, located in the direction of the constellation Ursa Major, is designated SDSS J091301.0+305120

This bizarre exiled star is zooming out of the Milky Way galaxy at more than one million mph. So far, five exiled stars have been located. These rogue stars are now being lumped under a new class of unusual space objects-called hypervelocity stars.

"These stars literally are castaways," said Smithsonian astronomer Warren Brown. "They have been thrown out of their home galaxy and set adrift in an ocean of intergalactic space."

Astronomers believe that thousands of castaway stars probably exist within our galaxy. By comparison, the Milky Way contains about 100 billion stars. The Smithsonian team examined dozens of stellar candidates across an area of sky almost 8,000 times larger than the full Moon to spot their quarry.

Exiled stars were probably thrown from the galactic center millions of years ago. Each star once was part of a binary star system. When a binary swings too close to a black hole, the intense gravity can yank the binary apart capturing one star while flinging the other outward at tremendous speed (hence the word hypervelocity).

Chances of seeing a rogue star at the moment it's being ejected are that good, according to Brown. But the hunt will continue as he and fellow astronomers are likely to find more examples of the stellar castaways.

The first castaway, SDSS J091301.0+305120, is traveling out of the galaxy at a speed of about 1.25 million miles per hour; it is located 240,000 light-years from Earth.

Castaway stars, traveling at hyper speeds through deep space, are located far from Earth. Their motion cannot be detected except with sophisticated electronic and optical instruments.

What's in the Sky: The Pleiades, also called the seven sisters, (Messier 45) is a naked eye star cluster in the constellation of Taurus. The Subaru (Japanese for Pleiades) automobile company was named for this star cluster. You can see the cluster best this weekend, in the east, just before midnight. Other fascinating stellar objects are also observable nearby. See accompanying sky map.

Lou Varricchio, M.Sc., is the NASA/JPL solar system ambassador for Vermont. He is available for school and community presentations.

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