There are three types of galaxies. It is developed by Edwin P. Hubble. The classification scheme is improved by famous astronomer Gerard de Vaucouleurs. They have divided into three types based on their size, extent of bars, an openness of spirals and size of the galactic bulges.
Spiral galaxies: It is the most common kind in the universe. Andromeda galaxy is located nearby our Milky Way galaxy. Milky Way galaxy comes under spiral type. The spiral consists of large rotating diskettes of nebulae and stars. Moreover, the spiral is completely covered by a shield of dark matter. The galactic bulge is the central bright area. It is located in the centre of the galaxy. Most spirals have an aura of star clusters and stars arranged below and above the disk. The barred spirals are those that have bright and large bars of stars. It will have a material that divides their central sections. The astronomers study about the majority of galaxies with these bars. They study to understand their functions and role they play in the galaxy.
Elliptical galaxies: It is egg shaped that is ovoid or ellipsoidal. It is mostly found in smaller compact groups and galaxy clusters. Mostly, elliptical consists of low mass and older stars. Do you know why? It is because the elliptical does not have dust clouds and star making gas. At present, there is a small star formation is seen in them. Ellipticals have about one hundred million to one hundred trillion stars. It occurs in different sizes and different numbers. One of the best examples to explain Elliptical galaxy is Messier 87.
Irregular Galaxies: As the name implies, the galaxy is irregular in shape. Small Magellanic Cloud is the best example for an irregular galaxy. It can be viewed from Earth. It does not have an appropriate structure to shape itself as elliptical or spiral.
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