What are galaxies? Give a detailed account of different types of galaxies.

Galaxies are collections of stars, dust, and gas rotating around supermassive black holes. A galaxy can range in the number of stars as well as its size. Small galaxies are called dwarf galaxies, can contain as little as tens of millions of stars whereas massive galaxies contain hundreds of trillions of stars.

There are three main types of galaxies: Elliptical, Spiral, and Irregular.

a) Elliptical galaxies: Elliptical galaxies are shaped like a spheroid (flattened shape), or elongated sphere. Most of the star in elliptical galaxies are very old and red in color. It is believed that elliptical galaxies are older than spiral galaxies. Elliptical are smaller in number and contain less dust than the spiral galaxy.

b) Spiral galaxies: The Milky Way is thought to be a spiral galaxy with a black hole at its center. Spiral galaxies comprise up to half of all the galaxies in the known universe. Most of the star are bluish and they are young.

c) Irregular galaxies: Irregular galaxies are classified into three main categories; Irr-I, Irr-II, and dIrr. It is believed that some irregular galaxies are deformed by the gravity of other galaxies.

Here are the structure of galaxy:-