Wednesday, October 16, 2013

Are there also galaxies racing towards us

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Although the universe as a whole is expanding, there are still galaxies moving in our direction-for example, the nearby Andromeda Galaxy which is travelling straight towards us at a rate of about 300km/sec.
    To understand this apparent contradiction we have to differentiate between two phenomena: on the one hand the motion of galaxies through space, on the other hand the expansion of the cosmos itself. Random motions of galaxies in space are typically in the order of a few hundred kilometers per second. For galaxies that are very close to our Milky Way galaxy, the expansion is negligible and random motions dominate. For more distant galaxies, random motions is negligible compared to that of expansion. Hence all distant galaxies seem to be rushing away from us as a result of expansion, whereas nearby galaxies can be moving either towards us or away from us.

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