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European Week of Astronomy and Space Science Meeting News and Video

Galaxies in a spin

22 Apr 2009, 16:58 UTC
Galaxies in a spin
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Why does our Galaxy, the Milky Way, spin? Our Sun orbits the galactic centre at a velocity of 225 kilometres per second. Conventional wisdom suggests that fast-rotating galaxies form when two galaxies of roughly equal size collide in a huge cosmic collision, which can often form ring galaxies where the core is separated from disc, or an elliptical galaxy. Thorsten Naab of the University of Munich reckons otherwise in the talk he's given at EWASS. He says that minor mergers - small galaxies colliding with larger galaxies - are more than capable instead of introducing sufficient angular momentum to speed up the rotation. Okay, big deal you might think. But consider this: the earliest galaxies ever seen, several thousand light years across, are rotating and nobody has ever been able to figure out how such young galaxies can form spinning discs. These galaxies were assembled from smaller galaxies merging with one another, and if Naab is correct, this is how they got their spin too. We can imagine the scenario wherein our Milky Way came together by swallowing up smaller galaxies and began to spin, a spin that continue to this day, 13 billion years later.

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