Collision may have influenced evolution of Milky Way

New research shows that an ancient collision between a small "sausage" galaxy and the Milky Way likely altered our galaxy and changed the way it evolved.
By Joseph Scalise | Nov 22, 2018
An international team of astronomers have uncovered evidence about an ancient collision between the Milky Way and a small object known as the "Sausage" galaxy, according to five new papers (1,2, 3, 4, 5) published in theMonthly Notices of the Royal Astronomical Society, The Astrophysical Journal Letters,and arXiv.org.

The crash is important because it likely defined the early history of the Milky Way and completely altered the galaxy's structure by creating both its inner bulge and outer halo.

Researchers state that between 8 and 10 billion years ago an unknown dwarf galaxy smashed into the Milky Way. At that time, the dwarf then split apart and scattered into many pieces that are still floating around today.

"The collision ripped the dwarf to shreds, leaving its stars moving in very radial orbits that are long and narrow like needles," explained co-author of one of the studies Vasily Belokurov, a researcher at the University of Cambridge, according to Phys.org.

Those stars are important because their paths move them close to the center of the galaxy, which suggests they came in on an eccentric orbit.

To analyze those movements, scientists studied data captured with the European Space Agency's Gaia satellite and plotted the velocity of the stars to see where they first came from. That reinforced the idea of an ancient collision.

The Milky Way still runs into other galaxies, including the small Sagittarius dwarf galaxy. However, the Sausage galaxy was much larger, which is why it had such an impact on the Milky Way's formation. Not only that, but the galaxy's disk likely fractured from the impact and needed time to regrow.

"While there have been many dwarf satellites falling onto the Milky Way over its life, this was the largest of them all," said Sergey Koposov, a researcher at Carnegie Mellon University.

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