Which type of galaxy is the Milky Way galaxy?
And the answer: spiral.
The Milky Way galaxy is a huge collection of stars, gas, and dust – our sun is just one of billions of stars swirling within the galaxy. If you look at the Milky Way from the top or bottom, it would look like a spinning pinwheel, which is why it's considered a spiral galaxy. It's estimated that two-thirds of galaxies in the universe are spiral in shape.
In the last century, we've learned quite a lot about our galaxy and those which surround it. Each galaxy is a collection of hundreds of millions (or even trillions) of stars, ranging in size from tens of thousands to hundreds of thousands of light-years across, and come in a variety of shapes. Besides the spiral formation with which we're more familiar, there are three other broad categories of galaxy shape: elliptical, peculiar, and irregular.
Spiral galaxies are characterized by broad, flat, rotating disks of stars, gas, and dust. The stars closer to the central bulge of the galaxy tend to be younger, redder stars, while those in the extended arms of the spiral are older and bluer. When we view these galaxies edge-on, we can observe the flat, disk-shape that is likely a result of their formation from clouds of dust and gas billions of years ago.
Elliptical galaxies are, well, elliptical in shape. Some are nearly spherical, resembling gigantic cotton balls of stars, while others are more elongated and resemble an American football. These galaxies lack distinct structure, and tend to appear puffier. Elliptical galaxies are also characterized by a lack of gas and dust, and are often populated with older stars. It's unclear how elliptical galaxies form, but scientists currently believe that they are the result of giant, galactic collisions.
Peculiar galaxies are essentially all due to collisions. Oftentimes, remnants of these collisions can be observed in parts throughout their whole, as smaller galaxies will draw in stars before flinging them away. This can result in a shape called a ring galaxy, with the culprit star in the center.
Finally, irregular galaxies are exactly what they're named for: small, shapeless, chaotically arranged galaxies that can be victims of collisions but are distorted to the point of an unrecognizable shape.
Learn more about galaxies below.