Spiral galaxies

Definition

Spiral galaxies are a type of galaxy characterized by their flat, disk-like shape with spiral arms winding outward from the center. They contain a mix of young and old stars, gas, and dust, making them sites of active star formation.

5 Must Know Facts For Your Next Test

1. Spiral galaxies are categorized into three main types: Sa, Sb, and Sc based on the tightness of their spiral arms and the size of their central bulge.
2. The Milky Way is an example of a barred spiral galaxy, classified as SBbc.
3. Spiral arms are regions with higher concentrations of gas and young stars due to ongoing star formation.
4. These galaxies often have supermassive black holes at their centers.
5. They make up about 60-70% of all observed galaxies in the universe.

Review Questions

• What distinguishes a spiral galaxy from other types of galaxies?
• How do astronomers classify different types of spiral galaxies?
• Why are the spiral arms important regions within these galaxies?

Related terms

Elliptical Galaxies:

A type of galaxy that is more spherical or oval in shape with little to no new star formation.

Barred Spiral Galaxies: A subtype of spiral galaxy that has a central bar-shaped structure made up of stars extending through its core.

Irregular Galaxies:

Galaxies that do not fit into the regular classifications like elliptical or spiral due to their irregular shapes and lack of defined structure.