Expert: Jayendra Upadhye - 2/1/2009

Question
Hello Jayendra Upadhye

Sometime ago, i read that the Andromeda galaxy is heading towards us. I believe i'm correct in saying that M81 and 82 are heading for a collision too. However, i have just been thinking. I thought all the galaxies were meant to be moving away from each other, due to the big bang?

Thanks
David

Answer
Hi,
David,
1 - The earth does pull us all. Correct?
2 - It also pulls at the moon and the satellites we put around it in
   earth orbit.
3 - Next the sun pulls all the planets including the earth. Right?
4 - On a greater scale, the galaxy holds a 100 billion stars in
   thrall!
5 - The local group consisting of over a dozen galaxies large and
   small is gravitationally bound like examples 1 thru 4 above, and
   is bound to merge sooner or later, to form a large elliptical
   galaxy.
6 - Our sun is not the original member of the milky-way, but has
   been captured from a small irregular galaxy near by.
7 - The whole local group is heading towards the Virgo super cluster
   of galaxies at about 300 Kilometer / sec.

When all this is true, We should understand that the local group SHARES hubble expansion, meaning they have same relative speed of recession, and so are free to interact gravitationally with each other. Like the earth and the moon falling around the sun in free fall, are free to pull at each other.

Galaxies much beyond the range of the local-group begin to show differential recession rates.

The Abell cluster shows a red shift 7 and is the farthest cluster of galaxies.

regards
Jayen