有什么星系类型？

Introduction and Review of Terminology

Alright so this lesson is on the types of galaxies that exist. But before we talk about the fun stuff, let's do a quick review of what a galaxy is to warm up our minds.

The General Types

Ok so let's test how much you know, do you know how many general (not-specific) types of galaxies exist?

So the four major types of galaxies are as follows.

1.) Eliptical

As you may note from their name, these galaxies have an ellipsoidal profile, giving them their signature elliptical appearance regardless of the viewing angle. Their appearance shows little structure and they typically have relatively little interstellar matter. Due to this, it should be noted that these galaxies also have a low portion of open clusters and a comparatively slower rate of new star formation. Therefore they are dominated by generally older, more developed stars that orbit the common center of gravity in random directions. Within the types of eliptical galaxies are also something that we call "shell galaxies" where the stars in the galaxy's halo are distributed in concentric shells. About a tenth of elliptical galaxies have a shell-like structure. The shell-like structures are thought to develop when a larger galaxy absorbs a smaller companion galaxy.

Fun Fact: The largest galaxies happen to be large elipticals!

2.) Spiral

These galaxies make up the stereotype of what a galaxy looks like. Even our own galaxy, the Milky Way, is a spiral galaxy! As you may note from their name, these galaxies resemble spiraling pinwheels. Though their visible interstellar materials lie mostly on a plane, the majority of mass in spiral galaxies exist in a roughly spherical halo of dark matter that extends beyond the visible component of the galaxy. Spiral galaxies consist of a rotation of stars and interstellar objects, along with a center composed of generally older stars (hence the analogy to the pinwheel).

Fun Fact: In spiral galaxies, the "arms" are shaped such that they resemble approximate logarithmic spirals!

3.) Dwarf

These galaxies, as their name may tell you, are small. Most being one hundreth the size of the Milky Way! Thus in comparison to other galaxies, they only contain a few billion stars. However, despite being little in size, they are large in number! Most of the galaxies in our universe are dwarf galaxies. These can be classified as either eliptical, spiral, or irregular.

Fun Fact: Many dwarf galaxies may orbit a single larger galaxy. For example, the Milky Way has at least a dozen such satellites, with an estimated 300–500 yet to be discovered!

4.) "Other"

These are the outcasts, the "rebels" shall we say. We have two specific types called the peculiar and the lenticular. A peculiar galaxy is a type of galaxy which is named due to their tendency of developing unusual properties due to tidal interactions with other galaxies. An example of this is the ring galaxy, has a seemingly a ring-like structure of stars and interstellar medium surrounding a central core. A lenticular galaxy, on the other hand, is a galaxy that has properties of both elliptical and spiral galaxies.

Fun Fact: Astronomers believe that the Andromeda Galaxy may be a ring galaxy!

Concluding Remarks

While it would be lovely to dive into the specifics of these galaxies even further, our time on this Earth (with our great technological developments) is still too short to give us much more information. The universe is vast, thus we have much more to explore! Hopefully you understood everything, and hopefully you enjoyed learning about the types of galaxies that are out there.