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?
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2$\begingroup$ Why would they be heavier? How massive do you consider our galaxy to be? $\endgroup$– Jon CusterCommented Oct 2, 2023 at 14:34
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$\begingroup$ I thought the old galaxies discovered were much larger than the Milky Way. But maybe I misunderstood. $\endgroup$– Tony HägerCommented Oct 2, 2023 at 14:45
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9$\begingroup$ 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. $\endgroup$– John RennieCommented Oct 2, 2023 at 15:05
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$\begingroup$ 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 $\endgroup$– QuilloCommented Oct 2, 2023 at 15:05
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$\begingroup$ @TonyHäger I'm reluctant to post an answer since this isn't my area, but giant galaxies might be more common than we think. $\endgroup$– John RennieCommented Oct 2, 2023 at 15:07
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2 Answers
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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.
answered Oct 2, 2023 at 15:07
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It depends what you consider a massive ancient galaxy.
I assume you're referring to the likes of the "universe breaker" galaxies, which are extremely distant high-mass galaxies that have a few hundred billion solar masses, and yes, taking mergers into consideration, they are very likely significantly heavier and larger today - probably within the trillions of solar masses now.
But we do have such galaxies in the more "nearby" universe. One of the most massive galaxies known, IC 1101, is an excellent example of this. It is just over one billion lightyears away and is significantly more massive than the universe breaker galaxies, with an insane weight of 2.5 trillion solar masses. This means it likely started its life as a high mass galaxy to begin with; Potentially similar to the ones we observe in the distant universe.
But on an even closer level, in the local local universe, we do still see some relatively extreme mass galaxies within the trillions of solar masses. Our own galaxy, the Milky Way is an example of such a structure according to this study, which places it at 1.5 trillion SMs (take with a grain of salt because these estimates change significantly every Tuesday)
So the point is that you are correct about the Universe Breaker galaxies being very large for their age, and that they indeed are probably much larger today. But for all we know, many major galaxies in our local universe were also part of this demographic, but we can't say for sure because the history of local galaxies are relatively uncertain and can only be estimated based on observations.
