Did Milky Way's Arms Swing the Sun 1,000s of Light Years from Its Origin?
A new simulation has put forth an explanation for how our Sun arrived where it has, and why it is so chemically different from the other stars around it. Research has seen some stars pushed into wild irregular and elongated orbits by the Milky Way galaxies arms, sending them well away from home. However our Sun has a nice clean circular path around the galactic center.
Astronomer Rok Roškar of the University of Washington in Seattle and colleagues have developed a computer simulation that suggests the Milky Way’s arms could have launched the Sun thousands of light years from its birthplace, but allowing it to maintain its circular orbit.
"Our results imply that a star like our Sun could have originated in an entirely different place in the galaxy than where it presently resides," says Roškar.
The computer simulation takes place over a billion years, harkening back to when scientists believe the Milky Way was last thought to have merged with another galaxy. The formation of the spinning galactic dish seemed to form spiral arms, and then destroy them, over the course of the simulation, as the disc grew, shifting the location of stars within the greater galaxy.
"This seems very surprising at first," said Roškar, speaking to New
Scientist. "Typically one would assume that if a star's orbit is
perturbed by something like a spiral arm, it would necessarily result
in a more elliptical orbit."
Scientists believe that this is caused as a result of a process called ‘co-rotational resonance’. Essentially, a star that is traveling behind a spiral arm will gain momentum and be flung further out, similar to a water-skier behind a boat as it turns. Conversely, a star that is placed in front of a spiral arm will be dragged backwards, seeing it slow in speed and thus dragged into the heart of the galaxy.
Johannes Andersen of the Niels Bohr Institute for Astronomy, Physics, and Geophysics in Copenhagen, Denmark, notes that “It is a nice piece of work,” but that confirming whether any of this has actually happened will be hard, considering that “the mechanism leaves no observable record in the orbits and velocities of stars.”
But nevertheless, Roškar and co believe that this migration technique might be at the route of up to 50% of the stars within our own Sun’s neighborhood. More evidence to back up or disprove this theory will be found in monitoring whether spiral arms to move, and not simply be static. However, "We don't yet know whether spiral arm[s] are transient or not," says Andersen.
Posted by Josh Hill
http://www.journals.uchicago.edu/doi/abs/10.1086/592231
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