Types of Galaxies

There are thousands of galaxies spread around the universe. Living in a big universe which is always expanding(even as we speak), how do we differentiate these galaxies. If your answer is shape. You are correct. Astronomers have come up with categories for each galaxy. Galaxies are categorize according to their shape. We have altogether three main types of galaxies.

The first one is the Spiral galaxy. For your information, Miky Way is a spiral galaxy. Spiral galaxy as you know is shaped like a spiral. According to NASA, spiral galaxy is shaped like a disk with a bulge in the center. The spirla galaxy also rotates slowly. Milky Way makes a complete revolution in every 250 million years or so. New stars are constantly forming in the nebulae of spiral galaxies. They are also the most common galaxy that can be found scattered around the universe.

Examples of spiral galaxy:
1)Andromeda (Messier 31, M31, NGC 224)



2)NGC 1300

The second type is the Eleptical galaxy. Eleptical galaxy, like the name suggests, has an eleptical shape ranging from spherical to elongated. Similar to the spiral galaxy, the eleptical galaxy also rotates but at slower speed compared to spiral galaxy. The amount of gas and dust in the eleptical galaxy are also less compared to spiral galaxy. Furthermore, the rate of new stars forming are also lower in eleptical galaxy. MOst of the stars in eleptical galaxy are old stars.

Examples of eleptical galaxy:
1)M87


2)M86



The last type of galaxy is the irregular galaxy. Unlike spiral and eleptical galaxy, this galaxy does not have any regular shape. It is also the most rare kind of galaxy in the universe. Any galaxy which have been classfied as irregular galaxy simply does not posses any structure that is in accordance to the Hubble classification. More classifications of the galaxy may exist in the future.

Examples of irregular galaxy:
1)Sextans A



2)Magellanic Clouds



Sources:
Wikipedia
NASA
Delphes
University of Arizona