Question on Galaxies

[Taff]

Hi' With a question on galaxies.Why is it that the galaxies are moving away from the milky way.And M31 is coming towards us Thanks.Mark

[ashenlight]

I THINK that M31 and our own galaxy are thought to be a bound pair in orbit around eachother... " Both galaxies formed close to each other shortly after the Big Bang initially moving apart with the overall expansion of the universe. But since they are bound to one another, they are now falling back back together and one very plausible scenario puts them on a collision course in 3 billion years" see here

Whilst the rest of the universe is not necessary moving AWAY from US but the space in between things in the universe is expanding (think how dots drawn on a deflated balloon move away from each other when you blow the balloon up), This partially answers your question but hopefully someone can give a better (and more coherent) answer!

Amanda

[Taff]

Thanks Amanda' for your reply to explain.Nicely written with you Thanks.Mark

[brianb]

Think of drunken ants running at random around the surface of a balloon which is being blown up. On average the ants will be moving away from each other but some pairs of ants - mainly those fairly close to each other - will in fact be getting closer together, at least for a short period of time. The Milky Way and M31 happen to be a pair of mutually approaching galaxies in a generally expanding universe.

As Amanda has hinted, the Local Group of galaxies (including the Milky Way, M31 & M33) is in fact apparently bound tightly enough by gravity to overcome the general expansion. In a few tens of billion of years, the Local Cluster may have "collapsed" into a single giant elliptical galaxy.

[Mutley]

Spot on Amanda. It's space that is expanding, not things moving away from each other - hence allowing some distant galaxies to have red-shifts indicating speeds greater than light.

[Doc]

We know that the universe is expanding because galaxies that are farther away from us have greater red shift (i.e., longer wave length) in their light than do galaxies that are closer. This is known as Hubble's Law, named for the astronomer who first realized that the magnitude of the red shift is correlated with distance. Red shift is a good measure of the galaxies velocity away from us - the faster it is moving the greater the red shift. Conversely, if a galaxy is moving towards us, such as M31 a part of the Local group we would see a blue shift (shorter wavelength) in its light. So it's not too difficult to tell that the universe as a whole is expanding.

[Taff]

Hi Brian' Thanks for your time and help to explain to me.Some times it is head scratching:icon_scratch:.Mark