Farthest stars in Milky Way probably stolen from another galaxy

Half of the 11 farthest known stars in our galaxy that are located about 300,000 light-years from Earth might have been ripped from another galaxy, U.S. researchers said Wednesday.

Researchers at the Harvard-Smithsonian Center for Astrophysics used computer models to simulate how the Sagittarius dwarf, one of dozens of mini-galaxies that surround our galaxy, might move over the past eight billion years, by varying its initial velocity and angle of approach to the Milky Way.

The study showed the Sagittarius dwarf started with a weight of about 10 billion times the mass of our Sun, or about one percent of the Milky Way’s mass.

However, over the age of the universe it made several loops around our galaxy, and on each passage, the Milky Way’s gravitational tides tugged on the smaller galaxy, pulling it apart like taffy.

“Five of the 11 most distant stars in our galaxy have positions and velocities that match what you would expect of stars stripped from the Sagittarius dwarf,” they said in a statement.

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“The other six do not appear to be from Sagittarius, but might have been removed from a different dwarf galaxy.”

Overall, the hapless dwarf might have lost about a third of its stars and a full nine-tenths of its dark matter.

This resulted in three distinct streams of stars that reach as far as one million light-years from the Milky Way’s center.

Mapping projects like the Sloan Digital Sky Survey have charted one of the three streams predicted by these simulations, but not to the full extent that the models suggest, the researchers said.

Future instruments like the Large Synoptic Survey Telescope, which will detect much fainter stars across the sky, should be able to identify the other streams, they added.

“The star streams that have been mapped so far are like creeks compared to the giant river of stars we predict will be observed eventually,” said lead author Marion Dierickx of the Harvard-Smithsonian Center for Astrophysics. “More interlopers from Sagittarius are out there just waiting to be found.”

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The findings have been accepted for publication in The Astrophysical Journal. (Xinhua)