Galaxy Types and Classification by Hubble, Himself
The Hubble Galaxy Classification is a system used to categorize galaxies based on their visual appearance.
Astronomers estimate there are possibly as many as 100 billion galaxies in the expanding universe.
Through telescope observation, each galaxy has a specific size, shape and structure. The morphology that galaxy has is the essence of the Hubble Galaxy Classification.
Let’s see some examples of Edwin Hubble’s galaxy classification scheme.
How the Hubble Galaxy Classification works
Galaxies are just large accumulation of stars. On the grand scale of things, the universe holds a mammoth collection of galaxies.
We know this because we observe them using the Kepler and Hubble Telescopes. Each galaxy is a collection of stars, planets and other solar remnant.
A supermassive black hole is at the galactic center. Galaxies are flat because things that rotate flatten out on the rotational access
Based on how galaxies flatten and spread out, astronomers classify these groups of stars as spirals, ellipticals, lenticular and irregular.
Spiral galaxy classification
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.
Our nearest neighbor is the Andromeda Galaxy and is a spiral galaxy as well. It’s classified as a SA(s)b galaxy classification.
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.
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.