“Magic mirror on the wall, who’s the fairest one of all?” -the Wicked Queen
For a galaxy, though, it’s really not fair to ask which one’s the fairest. It’s simply too subjective of a question. But size, now that’s something we can measure.
So, I ask you — galaxies of the Universe — to step forward and show yourselves! Galaxy, galaxy on the wall, who’s the largest one of all?
Nice try, Andromeda. Our biggest sister, Andromeda, has about 400 billion stars that make her up. That’s about 50% more than our Milky Way has, and it makes Andromeda the largest galaxy in our local group. Andromeda is about 2 million light years away from us.
But those are some small potatoes. If we want to find a bigger galaxy, we need to look at a bigger group of galaxies. Let’s try out the closest cluster to us…
The Virgo cluster! If we want the biggest one, we go straight to the heart of the cluster, which is where the giant elliptical galaxy — M87 — lives.
So let’s take a look at M87!
55 million light years distant, M87 is the largest and brightest galaxy in the Virgo cluster, and is notable for the huge, 5000-light-year-long jet coming from the supermassive black hole living at its core!
This galaxy is tremendous in its physical size: about 500,000 light-years in radius. As far as its massiveness, it’s about 200 times as massive as the Milky Way, or about 50 trillion times as massive as our Sun.
But what if we go to even bigger clusters than Virgo? Some of them are like the Coma Cluster, below.
The cluster is larger than Virgo, but what about its largest galaxy? Well, there are two giant elliptical galaxies close to its center, NGC 4889 and NGC 4874, easily visible in the above image. But even combined, they only add up to 20 to 30 trillion times the mass of our Sun.
On the other hand, there are spectacular galaxy clusters like the Perseus Cluster, which I’ll show you below.
Well, if we look at the heart of the Perseus cluster, we find the galaxy Perseus A, also known as NGC 1275. This is one spectacular galaxy:
(There’s a huge version of this, from Hubble, of course, available here.)
At a distance of 237 million light years, it’s really quite far! And while it is hugely bright in its X-ray emissions, it’s only about 100,000 light years in radius; only about 3 times the size of our Milky Way!
So some of these galaxies at the hearts of clusters are supermassive, loaded up with the matter from trillions of Suns in them, but others are much more modest.
So we go around, finding galaxy clusters, and look for giant, centrally-dominant elliptical galaxies in them. (Fornax, dominated by NGC 1399, is shown above.) And we measure their angular size, their light, and try to infer their masses.
So enough with the suspense, already! Who wins?
Say hello to cluster Abell 2029, a supercluster of galaxies just over a billion light years away. If we look at the heart of Abell 2029, we find the largest, most monstrous galaxy ever observed, IC 1101.
IC 1101 is 5 to 6 million light years across, or about 5 times larger in radius (and hence about 125 times larger in volume) than the huge M87!
Estimates of its mass are close to a quadrillion solar masses, with an estimated 100 trillion stars!
And — as of right now — it’s the largest galaxy we know of in the entire Universe. Enjoy!