The Crazy Cosmos: Stars Near Sun are Wild & Wayward

[On the Road]

A new survey of stars near the Sun reveals a wild and crazy past in which wanderers arrived from all directions under the gravitational influences of black holes, clouds of gas and invading galaxies.

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All stars in the Milky Way are gravitationally bound to the dense galactic center, around which they all orbit. Most are born in circular orbits, but when they encounter other objects, they can change course and speed up. Andersen told SPACE.com that older stars in particular move more rapidly than was known. "Something … has stirred up their motions more than we knew," he said.

But what did the stirring, giving each star a different trajectory and speed? Several things were probably at work giving gravitational boosts, according to a preliminary analysis of the data:

--The Milky Way's own spiral arms, which are denser than the relative voids in between
--Smaller galaxies falling into the Milky Way and being consumed
--Giant clouds of gas falling through the galaxy
--Black holes

http://www.space.com/scienceastronomy/milkyway_movement_040406.html