<p>Andromeda and the Milky Way are set to collide in 4bn years. Will the Local Group collide with M81, and what about further away groups? if so, when? </p>

CC BY-SA 3.0
2016-11-12T02:49:37.203Z
M81 is bound in a group of galaxies, so you should be asking is the M81 group bound to the Local group.  I had a quick look at the numbers and it is a close call.  Depends on exact mass-to-light ratios and complex interactions with other nearby groups.  But most likely, if they are bound, they would go into orbit about each other or merge to form a bigger group.
eshaya
CC BY-SA 3.0
2016-11-12T18:24:53.400Z
@eshaya while the period technically doesn't matter, I have to wonder if there's been time for a single orbit since the galaxies have formed?   I'd also ask whether dark energy makes orbits on that scale impossible.   I (think) the only options are merge, closer flyby or drift apart.   A galaxy or two of M81 group hitting our local group and most of it flying past also seems somewhat possible.   But accurate predictions?  I have no idea.
userLTK
CC BY-SA 3.0
2016-11-13T01:21:58.803Z
While this question is related but different, I found the answer well worth reading and with sufficient overlap:   http://astronomy.stackexchange.com/questions/6288/when-will-the-milky-way-arrive-at-the-great-attractor-and-what-all-happen-the?rq=1
userLTK
CC BY-SA 3.0
2016-12-08T01:31:01.033Z
@userLTK There has not been enough time yet for M31 to do one orbit around the MW, so I doubt M81 group has.  And, typically, on these scales  galaxies fall together into groups and groups fall into groups to form bigger groups.  How else do galaxy groups and clusters form?  Mergers mostly happened at an earlier time and from objects more closely spaced.  The M31/MW merger that is going to happen is a strange fluke due to the unusually low angular momentum of the pair.
eshaya
<galaxy><cosmological-inflation><local-group>
Is the M81 group bound to the Local group?
bandybabboon
# Is the M81 group bound to the Local group?

(Asked by: username_0 on 2016-11-11)

Andromeda and the Milky Way are set to collide in 4bn years. Will the Local Group collide with M81, and what about further away groups? if so, when?

**Tags:** galaxy, cosmological-inflation, local-group

> **Comments:**
> **username_1**: M81 is bound in a group of galaxies, so you should be asking is the M81 group bound to the Local group.  I had a quick look at the numbers and it is a close call.  Depends on exact mass-to-light ratios and complex interactions with other nearby groups.  But most likely, if they are bound, they would go into orbit about each other or merge to form a bigger group.  
> **username_2**: @username_1 while the period technically doesn't matter, I have to wonder if there's been time for a single orbit since the galaxies have formed?   I'd also ask whether dark energy makes orbits on that scale impossible.   I (think) the only options are merge, closer flyby or drift apart.   A galaxy or two of M81 group hitting our local group and most of it flying past also seems somewhat possible.   But accurate predictions?  I have no idea.  
> **username_2**: While this question is related but different, I found the answer well worth reading and with sufficient overlap:   http://astronomy.stackexchange.com/questions/6288/when-will-the-milky-way-arrive-at-the-great-attractor-and-what-all-happen-the?rq=1  
> **username_1**: @username_2 There has not been enough time yet for M31 to do one orbit around the MW, so I doubt M81 group has.  And, typically, on these scales  galaxies fall together into groups and groups fall into groups to form bigger groups.  How else do galaxy groups and clusters form?  Mergers mostly happened at an earlier time and from objects more closely spaced.  The M31/MW merger that is going to happen is a strange fluke due to the unusually low angular momentum of the pair.  

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## 0 answers

