[Nizzle (OP)]

What explains the fact that all galaxies are moving away from us... except one?
I thought I read somewhere else on this forum that everything's moving away from each other with a speed greater than escape velocity, yet somehow, that didn't work for Milky Way & Andromeda?

[Æthelwulf]

What explains the fact that all galaxies are moving away from us... except one?
I thought I read somewhere else on this forum that everything's moving away from each other with a speed greater than escape velocity, yet somehow, that didn't work for Milky Way & Andromeda?

Well, I think it is falling towards us at 300,000 meters per second or something like that. It maybe a matter of relativity however that we can measure atleast some galaxies moving towards us.

This really is a good question, high standards indeed because I don't know the answer.

[Æthelwulf]

meters sorry, meters... even that is probably wrong haha

[Soul Surfer]

Simulations of the effects of gravity on the largest scales in the universe suggest that material tends to clump together in knots and strings do we see large galaxy clusters and strings of higher densities of galaxies streaming towards the clusters and very large volumes with very little material or galaxies in them.  This means that on a local scale galaxies tend to be approaching each other and it is only at distances far greater than the separation of large clusters that the expansion of space generally becomes the dominant factor.  As far as can be measured everywhere in the universe local velocity differentials are in the range zero to plus or minus 1000 Km/sec this is very low compared with the red shift velocities which can be a significant fraction of the velocity of light (300,000 Km/sec) around 100 times faster

here is quite a good simulation video with french commentary
tp://www.youtube.com/watch?v=YVG6hqsVLr4&feature=related

[Æthelwulf]

Simulations of the effects of gravity on the largest scales in the universe suggest that material tends to clump together in knots and strings do we see large galaxy clusters and strings of higher densities of galaxies streaming towards the clusters and very large volumes with very little material or galaxies in them.  This means that on a local scale galaxies tend to be approaching each other and it is only at distances far greater than the separation of large clusters that the expansion of space generally becomes the dominant factor.  As far as can be measured everywhere in the universe local velocity differentials are in the range zero to plus or minus 1000 Km/sec this is very low compared with the red shift velocities which can be a significant fraction of the velocity of light (300,000 Km/sec) around 100 times faster

here is quite a good simulation video with french commentary
tp://www.youtube.com/watch?v=YVG6hqsVLr4&feature=related

Kilometers damn it!

[Æthelwulf]

Simulations of the effects of gravity on the largest scales in the universe suggest that material tends to clump together in knots and strings do we see large galaxy clusters and strings of higher densities of galaxies streaming towards the clusters and very large volumes with very little material or galaxies in them.  This means that on a local scale galaxies tend to be approaching each other and it is only at distances far greater than the separation of large clusters that the expansion of space generally becomes the dominant factor.  As far as can be measured everywhere in the universe local velocity differentials are in the range zero to plus or minus 1000 Km/sec this is very low compared with the red shift velocities which can be a significant fraction of the velocity of light (300,000 Km/sec) around 100 times faster

here is quite a good simulation video with french commentary
tp://www.youtube.com/watch?v=YVG6hqsVLr4&feature=related

Kilometers damn it!

I always get that wrong!!!!!

[CliffordK]

Keep in mind that everything in space would have a 3-D direction to its movement. 

It is easiest for us to determine the direction component of the vector towards us or away from us with the redshift/blueshift.  It is more complex to determine the vector component tangent to us. 

Also, keep in mind that the Milky Way will have moved in 3 billion years. 

I think any prediction of a collision between the two galaxies would be a longshot.

As far as why Andromeda is moving towards us.  Perhaps our technology of using Redshift/Blueshift for determining both distance and directionality precludes finding distant galaxies with a significant component of motion towards us compared to other galaxies in their local cluster.

[Æthelwulf]

Keep in mind that everything in space would have a 3-D direction to its movement. 

It is easiest for us to determine the direction component of the vector towards us or away from us with the redshift/blueshift.  It is more complex to determine the vector component tangent to us. 

Also, keep in mind that the Milky Way will have moved in 3 billion years. 

I think any prediction of a collision between the two galaxies would be a longshot.

As far as why Andromeda is moving towards us.  Perhaps our technology of using Redshift/Blueshift for determining both distance and directionality precludes finding distant galaxies with a significant component of motion towards us compared to other galaxies in their local cluster.

A long shot?

We only observe a very small portion of the universe. In other words, if we actually saw a collision, I'd mark it as a coincidental success.

[Æthelwulf]

Keep in mind that everything in space would have a 3-D direction to its movement. 

It is easiest for us to determine the direction component of the vector towards us or away from us with the redshift/blueshift.  It is more complex to determine the vector component tangent to us. 

Also, keep in mind that the Milky Way will have moved in 3 billion years. 

I think any prediction of a collision between the two galaxies would be a longshot.

As far as why Andromeda is moving towards us.  Perhaps our technology of using Redshift/Blueshift for determining both distance and directionality precludes finding distant galaxies with a significant component of motion towards us compared to other galaxies in their local cluster.

A long shot?

We only observe a very small portion of the universe. In other words, if we actually saw a collision, I'd mark it as a coincidental success.

Collisions like this only happened very very early in the universes history, no less.

[CliffordK]

Actually, the Milky Way collides with small galaxies all the time, and is incorporating several smaller galaxies into its structure right now.

http://en.wikipedia.org/wiki/Canis_Major_Dwarf_Galaxy
http://en.wikipedia.org/wiki/Sagittarius_Dwarf_Elliptical_Galaxy

Perhaps it is more rare with two large galaxies like the Milky Way and Andromeda colliding, but it does happen. 

Measurements of galaxies in deep-field surveys made by NASA’s Hubble Space Telescope generated a broad range of results: anywhere from 5 percent to 25 percent of the galaxies were merging.
[...]
Small galaxies were coalescing with large galaxies more frequently. In one of the first measurements of smashups between dwarf and massive galaxies in the distant universe, Lotz’s team found these mergers happened three times more often than encounters between two hefty galaxies.

This would seem to indicate that there are still quite a few large collisions.

[Æthelwulf]

Actually, the Milky Way collides with small galaxies all the time, and is incorporating several smaller galaxies into its structure right now.

http://en.wikipedia.org/wiki/Canis_Major_Dwarf_Galaxy
http://en.wikipedia.org/wiki/Sagittarius_Dwarf_Elliptical_Galaxy

Perhaps it is more rare with two large galaxies like the Milky Way and Andromeda colliding, but it does happen. 

Measurements of galaxies in deep-field surveys made by NASA’s Hubble Space Telescope generated a broad range of results: anywhere from 5 percent to 25 percent of the galaxies were merging.
[...]
Small galaxies were coalescing with large galaxies more frequently. In one of the first measurements of smashups between dwarf and massive galaxies in the distant universe, Lotz’s team found these mergers happened three times more often than encounters between two hefty galaxies.

This would seem to indicate that there are still quite a few large collisions.

Ok.