Is it also roughly the limit where gravity will be able to overcome space expansion? In other words, we can only hope to get to there, or at least see them, in the very far future?

  • $\begingroup$ Isn't the fact that there are galaxy blue shifted relevant to your question? $\endgroup$ – Alchimista Mar 4 '19 at 17:52
  • $\begingroup$ I don't really get what you meant, sorry. $\endgroup$ – longtry Mar 5 '19 at 9:47
  • $\begingroup$ Sorry I took " to" for "in" in title. That is why I was concerned about why you didn't think extragalactic stuff into account. $\endgroup$ – Alchimista Mar 5 '19 at 10:10
  • $\begingroup$ It's ok. Now that it's clearly understood, do you happen to know the answer to that question? It's been bugging me... $\endgroup$ – longtry Mar 6 '19 at 15:22
  • $\begingroup$ No but I am surprised that you cannot find some listed. $\endgroup$ – Alchimista Mar 6 '19 at 16:21

My impression is that, aside from the very rare galaxy that is moving towards us, only stuff inside the local galactic gravitational field can be blueshifted. Written perhaps more clearly, from spaceanswers ,

Andromeda is not the only galaxy to be moving towards us. With the help of galaxy surveys, astronomers have found that around 100 galaxies are moving towards us. Compared to the numbers of galaxies that we know of (hundreds of billions), blue-shifted galaxies are seemingly quite rare. Those that are moving towards us are either part of our Local Group, which means that we are gravitationally connected to each other, or they are found in the Virgo Cluster which everything in our Local Group is moving towards. The galaxies M90, M86 and M98 are all in the Virgo Cluster and all show blue shifts.

  • $\begingroup$ So does that mean all those 'superclusters' and 'great wall', 'Laniakea', 'filaments' are just fancy stuffs? I mean, knowing the structure of the universe is really cool - I love it too - but it doesn't have practical use because we can never reach redshifted galaxies. $\endgroup$ – longtry Mar 5 '19 at 9:50
  • $\begingroup$ @longtry besides that is already difficult to travel within the solar system, it is not clear unless shifting to scifi what a practical use of cosmology should be. In an expansion scenario one can indeed conceive future beings let with a star and a big,even more mysterious than now, black space, and nothing else to study. They will have no clue of expansion, even, or perhaps think of being the centre of an otherwise empty expanding bubble. $\endgroup$ – Alchimista Mar 5 '19 at 10:23
  • $\begingroup$ We'll only have stuffs of the Virgo cluster to 'play' with. It's ok in general, but it didn't answer my original question of what the furthest not redshifted object is? $\endgroup$ – longtry Mar 6 '19 at 15:20
  • $\begingroup$ The Virgo Cluster as a whole is redshifted, and most individual galaxies in the cluster have redshifts. Some galaxies in the cluster are moving fast enough within the cluster, in directions towards us, that the combination of (Doppler) blueshift from their local (peculiar) velocity and cosmological redshift (from the expansions of space between us and the cluster) results an overall blueshift. $\endgroup$ – Peter Erwin Mar 9 '19 at 15:24

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