Galaxies
What are Galaxies?
According to the Google dictionary, galaxies are a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction. “According to the best estimates of astronomers there are at least one hundred billion galaxies in the observable universe (www.physics.org).”
What are the Types of Galaxies?
There are four types of galaxies:Spiral, Elliptical, Barred Spiral, and Irregular.
“Spiral galaxies consist of a flat, rotating disc containing stars, gas and dust, and a central concentration of stars known as the bulge(en.wikipedia.org/wiki/Spiral_galaxy).” The Milky Way is an example of this type.
“An elliptical galaxy is a type of galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. Unlike flat spiral galaxies with organization and structure, they are more three-dimensional, without much structure, and their stars are in somewhat random orbits around the center (en.wikipedia.org/wiki/Elliptical_galaxy).” Elliptical galaxies are small dwarf galaxies that are a fraction of the size in mass of the Milky Way.
“A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in approximately two-thirds of all spiral galaxies (en.wikipedia.org/wiki/Barred_spiral_galaxy).”
“An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy (en.wikipedia.org/wiki/Irregular_galaxy).”
