A galaxy is a big system composed by stars, interestelar gas, solar systems planets, dark matter and dust. There are different sizes of galaxies, some of them, the small ones, have like a thousand stars, the big ones can have over a hundred billon or hundred trillon stars.
Some galaxies have black holes, which are a sort of mistery for the human beings (they are like a spacetime region with a intense gravitational power that atract everything around it, and nothing can escape from it).
There are around 200 billon galaxies in the universe, maybe more, every year, more galaxies are discovered. The most distant observed galaxy is about 13 billon light years from the planet Earth, a distant imposible to messuare with the human mind.
Our planet Earth is situated in a Solar System that is located in an small dot in the massive “Milky way” galaxy, our galaxy. It is composed for hundred of stars and one of those is our Sun.
Types of Galaxies
The most popular types of galaxies, according to their morphology, are elliptical, spiral and irregular.
This type of galaxy is composed of old stars and doesn’t have interstellar dust or gases, for that reason has a very low production of new stars. There are different sizes of elliptical galaxies, the big ones are made by collision and union of galaxies.
Using the catalog created by Hubble, the galaxies called spirals are made of two or more arms, giving it the spiral form. Like the stars, the spiral arms that characterize this galaxy, rotate around the center. Our solar sistem is located in a Spiral galaxy known as the Milky Way.
This type of galaxies is composed of the galaxies that can’t be classified into an elliptical or spiral galaxy. This type doesn’t fit in an structure; it doesn’t possess any defined shape.