Types of GalaxiesJul 01, 2016
There are three main shapes astronomers see when looking at galaxies. There’s a spiral shape, elliptical shape, and irregular, which means the galaxy has no definitive shape or symmetry.
Spiral Galaxies, as you can probably guess from the name, has a spiral pattern and visible components parts. Spiral galaxies have three main component parts: the bulge, the disk, and the halo. The bulge of a spiral galaxy is typically spheroidal in shape and it contains older stars. The disk of the galaxy contains younger and hotter stars and make up the spiral arm structures that distinguish the shape of a spiral galaxy. The halo hovers around the bulge and contains globular star clusters that are older than the stars seen in the disk. Our own home galaxy, the Milky Way, is classified as a spiral galaxy.
Elliptical galaxies, like spirals, are named for their shapes: they look like fat, fuzzy footballs. Instead of spreading out into a thin disk, as they do in spirals, the stars in an elliptical galaxy wrap completely around the galaxy's heart in all directions. These galaxies are composed of older stars, and new star formation ceases to occur. The largest galaxies that have been observed are elliptical in shape.
Irregular galaxies have no definitive shape. Some have hot, young stars, while others have lots of dust that obscures much of the galaxy. Irregular galaxies are often small in size, with only 1 million to billions of stars. By comparison, our own Milky Way galaxy is estimated to have 200 to 400 billion stars. The Large and Small Magellanic Clouds are two irregular galaxies that lie close to our own Milky Way Galaxy and can be observed in the sky from the southern hemisphere.
Watch the video attached to learn more about galaxies!