Recently the James Webb space telescope detected six massive ancient galaxies. They are very old and very far away. But these galaxies must still exist today and be even heavier now. Why can't we see any such huge galaxies near us now?

  • 2
    $\begingroup$ Why would they be heavier? How massive do you consider our galaxy to be? $\endgroup$
    – Jon Custer
    Oct 2 at 14:34
  • $\begingroup$ I thought the old galaxies discovered were much larger than the Milky Way. But maybe I misunderstood. $\endgroup$ Oct 2 at 14:45
  • 8
    $\begingroup$ The largest of the galaxies found is though to have been 60% more massive than the current Milky Way, and that was 13 billion years ago so it has presumably spent the last 13 billion years growing by consuming smaller galaxies (as the Milky Way had done). So this seems an entirely reasonable question and I can see no justification for the downvote or the snarky comment. $\endgroup$ Oct 2 at 15:05
  • $\begingroup$ I agree with @JohnRennie on the fact that it's a legit question. I am not an expert but (maybe) if they are big they are rare, so it's unlucky to find one close by (if you look distant the enclosed volume increases, so even "rare things" tend to show up). It's worth checking this nice answer, it could give some good ideas: physics.stackexchange.com/a/153865/226902 $\endgroup$
    – Quillo
    Oct 2 at 15:05
  • $\begingroup$ @TonyHäger I'm reluctant to post an answer since this isn't my area, but giant galaxies might be more common than we think. $\endgroup$ Oct 2 at 15:07

1 Answer 1


ESO 383-76 has a diameter of about 540.89 kiloparsecs and a mass of $2.3\times 10^{14} M_\odot$; it is around 200 megaparsecs away from us. There are many massive galaxies visible in the vicinity/present era.

It is just that the galaxies that were massive in the early universe (and presumably have accreted even more mass now by infalling smaller galaxies) have been moved to large distances: the redshift-scale factor conversion $1/a=1+z$ means that a $z=13.2$ galaxy is now 14.2 times further away, and the density of such early galaxies is $1/14.2^3=0.00035$ of what it was. So it is not surprising that we mostly see more recent, smaller galaxies.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.