What is the Largest Galaxy?

by Fraser Cain on May 11, 2009

Abell 2029. Image credit: Hubble

Abell 2029. Image credit: Hubble


Galaxies can range in size from having just a few million stars to well over a trillion stars. But have you ever wondered, what’s the largest galaxy in the Universe. The Universe is a big place, and we’ll probably never be able to see every single galaxy. So we can never know for sure what the biggest galaxy is. Instead, we’ll have to go with, what’s the largest galaxy that we know of?

The largest galaxies in the Universe are the giant elliptical galaxies. These are large, egg-shaped galaxies with trillions of stars. They’re formed through multiple collisions between smaller spiral galaxies of similar size. For example, when our own Milky Way collides with the same sized Andromeda Galaxy in a few billion years, the outcome will probably be a giant elliptical galaxy, with about a trillion stars.

The galaxies that can get the largest are the ones at the very center of galaxy clusters. Astronomers call these cD galaxies (for giant diffuse galaxies), or bright cluster galaxies. The grow by gobbling up any galaxy that comes too close to them, and since they’re at the center of a galaxy cluster, many galaxies get too close. In fact, these galaxies have a large space around them where astronomers can’t find any smaller galaxies; they’ve all been consumed by the larger galaxy.

A large cD galaxy can be 10 times brighter than the Milky Way, with about 100 times as much mass. They can have a diameter of 6 million light-years across (the Milky Way is about 100,000 light-years across).

An example of this is the central galaxy in the cluster Abell 2029.

It’s probably that there are even larger galaxies out there. And if they are there, you’ll find them at the center of the largest galaxy clusters.

We have written many articles about galaxies for Universe Today. Here’s an article about research into the galaxy cluster Abell 2029.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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