The 3 types of galaxies are:
- Irregular and Lenticular
Galaxies are just large accumulation of stars, planets and other solar remnant. Astronomers estimate as many as 100 billion galaxies in the expanding universe.
We observe galaxies using the Kepler and Hubble Telescopes. Galaxies are flat because things that rotate flatten out on the rotational access. Let’s see some examples of Edwin Hubble’s galaxy classification scheme.
1. Spiral Galaxy Classification
Two examples of the spiral galaxies are:
- The Milky Way
- The Andromeda Galaxy
MILKY WAY: The entire Milky Way galaxy rotates in a clockwise direction. Its disk contains dust, stars and gas rotating from a center point. The Milky Way is a flattened disk with spiral arms. The sun that provides heat to our planet belongs to one of the arms in the barred spiral galaxy. According to the Hubble Galaxy classification scheme, the Milky Way is a SBc barred spiral galaxy. Astronomers believe that it’s part way between SBb and SBc.
ANDROMEDA GALAXY: Our nearest neighbor is the Andromeda Galaxy and is a spiral galaxy as well. It’s classified as a SA(s)b galaxy classification.
2. Elliptical galaxy classification
Elliptical galaxies are circular in shape and elongated in a particular axis. The degree of ellipticity varies from E0 (circular) to E7 (elongated).
Elliptical galaxies have a smooth gradient for brightness. That is, brightness progressively dimmers away from the center of the galaxy.
This bulge of light at the center is a key difference between elliptical galaxies and other types of galaxies.
3. Irregular and lenticular galaxies
Irregular galaxies lack any form of symmetrical structure. They are unlike spiral galaxies because they don’t have distinct rotating arms. They are also unlike elliptical galaxies because they don’t have a definite center bulge.
Irregular galaxies commonly have clouds of dust and cannot be characterized in the Hubble Galaxy Classification system.
Similarly, lenticular galaxies are more of a transitional type of galaxy. They have lost most of their interstellar matter and are not forming stars of their own.