|
My understanding is that the expansion of space time does NOT affect the local group, or any other galaxy cluster. Andromeda is unaffected by the expansion of space time as demonstrated by Hubble. This is because this expansion is overcome by the effects of the local gravity field. If you took the expansion of space time away tomorrow Andromeda would still be speeding towards the Milky Way at the same speed as now, as this is driven purely by gravity and not by the "Hubble flow". Conversely, if it wasn't for the gravitational attraction within the local group, then Andromeda would be accelerating away at the rate of the Hubble flow, just like the rest of the Universe.
The gravitational effect within clusters is called the "peculiar velocity" and it is only when you get beyond the local group of galaxies do you observe the effect of the Hubble flow expansion of space time. All galaxy clusters will maintain some sort of integrity in spite of the expansion of space time, due to the effects of local gravity, principally from their dark matter halos.
Eventually, all the visible galaxies and galaxy groups will expand over the edge of the visible universe and we will be just left with the local group of galaxies to observe in our telescopes, or rather what is left of them after various merger events and exhaustion of their gas and dust through star formation.
|