Our sun may have been a galactic hitchhiker.

From LiveScience:

Astronomers have long believed that most stars are homebodies which stick close to their birthplaces. But a new simulation supports the suggestion that our sun might have once hitchhiked through the galaxy.

Where our sun or another star ends up migrating seems to depend on its position in a spinning spiral galaxy. Stars tagging along behind a massive spiral arm can get a gravitational speed boost that sends them into a bigger orbit around the galactic center. The stars leading in front of a spiral arm may end up getting slowed by the arm's gravitational pull and fall back into a smaller orbit.