More than 2 trillion galaxies in the universe, at least 10 times as many as we thought

The paper published in the Astronomical Journal does not reference any “merging” of ancient galaxies as alluded to by Glaurung above nor that the number of galaxies in the observable universe is around 200 billion (the standard figure for about 20 years now) and also mentioned by Glaurung.

The paper is clear that most of the galaxies likely to exist in the universe cannot be seen, about 90% of them according to the paper, but that they are out there as can be inferred using the 3-D modelling technique from the University of Nottingham, and also described in the paper.

So yes indeed, the universe seems to hold ALOT more galaxies than anyone previously imagined. And that means alot more stars and alot more planets.

Carl Kruse

Phil Plait in his Bad Astronomy column says this:

Oh, there is another thing, and this one is the coolest of them all. Because we now know how many galaxies there are, how they’re distributed throughout the Universe, and roughly how big they are physically, it’s possible to calculate how much of the sky is covered in galaxies. Think of it this way: If you’re in a very thinly populated copse of trees, you can look around and see things outside the copse; buildings and such in the distance. But if you’re deep within a forest of trees, everywhere you look you see trees.

So the researchers did this, and they found an astonishing thing: Given all the numbers they calculated, it looks very much that every single part of the sky is covered at least in part by a galaxy!

Do you see what this means? No matter where you look — up, down, left, right — and no matter how much you magnify the view through a telescope, at some point wherever you’re looking there’s a galaxy. It might be close by, or more likely crushingly far away, but it’s out there.

The sky is literally covered in galaxies.


That’s good for about 700 billion trillion stars, and heaven knows how many planets.

And still no place for me to call home…


i bet there’s a boatload of universes too.

1 Like

That is inaccurate. @Glaurung is correct. The article on the NASA website that Rob’s linked to in his original post is not very clearly written. Here is the original study it refers to for anyone interested…

That is accurate. They cannot yet be seen. Because their light has been red-shifted by the expansion of the universe beyond the red-shift magnitude visible to current telescopes. The James Webb Space Telescope is expected to detect many more of them.

The observable universe yes. But, again, the observable universe is a cross-section of it’s history where distance from us is inversely proportional to the age at which we observe any given volume.

That’s partially correct. The mass of the observable universe has long estimated to be significantly more than the mass of visible galaxies (even accounting for dark matter holding those galaxies together), but the number of those galaxies, their size and their properties was and still mostly is unknown, and known to be unknown.

Inconclusive. If the current model of galaxy evolution is correct, then the overall number of stars and planets is roughly the same (with the caveat that the rate of star formation, the average size of the stars formed, and consequently whether and how many planets are likely to orbit them, likely changes as galaxies evolve). However, all astronomers and cosmologists really have for now is this larger estimate of the early number density of galaxies, and the best current models for how they evolve. More of these faint galaxies will have to be observed with the next generation of space telescopes to fill in the gaps in astronomy’s knowledge of how so many faint distant galaxies evolved onto the kind of older galaxy population we observe in the volume of the universe nearer to us.

Sorry, no offense intended.


Section 4.3 of the paper discusses merging and states that the total number of galaxies now existing is probably 7 times less than the total number in the “observable universe.” So you’re partially correct, 200 billion is too small a number.

Section 4.2 crunches the numbers two different ways and gets between 1.2 trillion and 2 trillion for the total number of galaxies in the “observable universe.” Again, the observable universe includes distant galaxies that we are only able to see as they were billions of years ago, which have long ago evolved to be much different (through mergers) than how we see them.

The number of stars and planets in the universe depends on the number and average size of galaxies, but as this paper shows, those numbers have varied over time, so to get a realistic estimate we have to pick an age of the universe at which we make our measurements (say, out to 5 billion light years away) and then extrapolate from that for the parts of the universe which we can only see at a much different epoch.

Astronomy is tricky because of the time travel aspect of looking at ancient light from very far away. It’s hard to remember that the statements about the “observable universe” are not really statements about the universe as it exists now, but rather statements about the universe as it can be seen now, ranging from nearby galaxies that we see as they were only a few million years ago to distant galaxies that we see as they were at the dawn of time 10+ billion years ago.


IIRC, If you do the math on the event horizon of a black hole with the mass of the universe, you discover that such a black hole would be fifteen or twenty billion light years in radius. So, in essence, we are all living inside a gigantic black hole that contains the entire universe.


I remember reading speculative cosmologies that contemplates a wraparound universe like what you describe. The problem is that if we looked far enough out and saw ourselves from behind, because of the time travel aspect of astronomy, we’d be seeing our local neighbourhood of galaxies as it was many billions of years ago… which means no, we wouldn’t recognize that our view had wrapped around.


It’s beyond boggling - it can smash your mind to bits. I counsel against well-informed contemplation of the scale of things while tripping balls.


“Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist, but that’s just peanuts to space.” ~ Douglas Adams, The Hitchhiker’s Guide to the Galaxy


I know what that’s from, but I still couldn’t resist reading it in Donald Trump’s voice


Stop it.


That’s called a closed universe, i.e. one with positive curvature of spacetime. Cosmologists have some ways to estimate this curvature, for instance by analyzing the scale of variations in the cosmic microwave background radiation. It turns out that our spacetime appears rather flat. This means that if the universe is closed after all, it must only appear flat because it has a tremendously huge volume, many times that of the observable universe. So, it’s a good question! But it has been ruled out by observation.


1 Like

This topic was automatically closed after 5 days. New replies are no longer allowed.