Galaxies are huge groups of stars orbiting a central point. Almost always, that point is a supermassive black hole. Its pull keeps stars clustered into a galaxy which is central to the structure of the Universe.
How are Galaxies Formed?
Whenever we see something spectacular – mountains, planets, etc. – our first question is how it got there. For galaxies, the answer is pretty simple: gravity. But to understand why this is our answer, we actually have to go back in time. Most galaxies are already well-formed. So, into the time machine we go.
Early Universe – Matter Clusters Together
Welcome to the early Universe! Enjoy your time here, although there’s not much to do. Really, there’s not much to see either. Sure, there’s a ton of matter, but it’s not concentrated. It exists mostly in the form of dense clouds, called nebulae.
Admittedly, this place is kind of boring. But, let’s fast forward a bit. Over time, cloudy nebulae began to cluster around central points with strong gravity. As more things arrived at these centers, their gravity got even stronger. Soon, they became enormous!
So enormous, in fact, that all the stuff would collapse into a black hole! This would act as a more stable center of gravity, allowing things to orbit from a distance. And so, we have our galaxy.
But what about all the things in it? At the same time as the galaxies were beginning to take shape, stars started to appear slowly. Yet, they weren’t like the ones we recognize (at first). Those like our sun formed late, and on the outer part of galaxies. In the Milky Way, that means in the spiral arms.
Types of Galaxies
There are two main categories of galaxies. The kind we know best are spiral galaxies (the Milky Way is one).
The main feature of spiral galaxies is, as their name suggests, their spiral shape. At their center is a very bright circle with tons of old stars. Yet, their spiral arms are full of young and forming ones. These stars undergo drastic changes as they grow, generating a lot of light. This is actually what makes the spiral arms of a galaxy visible.
The second kind of galaxy is one we’re maybe less familiar with. It’s shaped like an elliptical, or a stretched-out circle. The stars in it orbit the center in random directions. Among them are actually some of the oldest stars in existence.
Notably, elliptical galaxies can be enormous. The largest, IC 1101, is 6 million light years across. That means that it takes light 6 million years to get from one side of IC 1101 to the other.
How Many Galaxies in the Universe
Now, I’d hate to throw another big number at you. But to answer this question, I have to. That’s because there are at least 200 billion galaxies in our Universe. 200 billion! We can hardly get out of our own atmosphere and there’s that much else to explore.
This should cause us to wonder: What might we still discover? The overwhelming size of the Universe means that it’s full of opportunity. Who knows, maybe one day you will explore it! If that sounds interesting, consider becoming an astronomer or an astronaut.
Although, whether or not you do, the future is bright. Space holds so much for us to see.
In fact, it holds SO much that those things often collide. Galaxies are no exception. Our very own galaxy is set to collide with another (the Andromeda Galaxy).
But relax, not any time soon! This collision won’t happen for another 4 billion years.
Still, other galaxies are crashing into each other all the time. When they do, they might merge to form an even larger galaxy. The result is almost always elliptical which is actually what allows elliptical galaxies to be so large. They just keep adding more and more stars through repeated collisions.
Other Great Resources:
More on Galactic Collisions: https://www.nasa.gov/image-feature/goddard/2017/hubbles-front-row-seat-when-galaxies-collide
The Andromeda-Milky Way Collision:
Facts about the Milky Way:
‘Fun Galaxy Facts for Kids’: http://www.ouruniverseforkids.com/galaxies/