Galactic Shapes

Spiral Galaxies

Both the Milky Way and our closest neighbor, the Andromeda Galaxy, along with many others, are known as spiral galaxies. In terms of the general shape, this means that both galaxies have a "swirl" to their structure, resembling what a cup of water looks like if you swirl it long enough. Throughout spiral galaxies, there's plenty of interstellar material and gas between stars, especially in the disks.

The spiral arms on the edges consist of many of the brightest stars in the galaxy. There are also many bright nebulae in the spiral arms usually which indicates a plethora of new stars being formed continuously.

Barred Spiral Galaxies

So, there are ordinary spiral galaxies but most of them have a bar going through them, hence the name "barred spiral" galaxies. These have a larger central bulge, wider galactic disk, and shorter spiral arms. This makes them look a lot more like elliptical galaxies. However, they retain most of the same properties as spiral galaxies.

Elliptical Galaxies

Elliptical galaxies take on the shape of spheres and ellipsoids mainly. Unlike spiral galaxies, elliptical galaxies don't contain spiral arms. They mainly contain older star populations and are dominated by globular clusters. A globular cluster is a dense collection of old stars due to the long-term effects of gravity. This makes sense from the image because most elliptical galaxies are tightly concentrated ellipsoids or spheres. Since most elliptical galaxies are mainly just systems of globular clusters, there isn't much interstellar material and nebulae found within these galaxies. This makes sense because most stars in elliptical galaxies are old so if there aren't many young stars, there can't be many places, like nebulae, that form stars inside an elliptical galaxy.

While elliptical galaxies themselves aren't overly common, dwarf elliptical galaxies are the most common type of galaxy. A dwarf elliptical galaxy is a galaxy that is elliptical but not very luminous(bright). They also tend to be significantly smaller than most other elliptical galaxies.

Irregular Galaxies