What is a Galaxies? | Types, Definition, Structure, Function & Facts
What is a Galaxy?
Galaxies are a group of stars and other space objects. Stars tend to revolve around a high center of gravity, like planets around the Sun in the solar system. Galaxies are very large and can contain trillions (more than billions!) of stars.
As large as galaxies are, they are often separated by vast expanses of empty space. There are even clusters of galaxies separated by even larger regions of space. Scientists believe there are more than 100 billion galaxies. Wow, the universe is so big!
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Scientists used to think that all the stars in the universe were part of a giant group of stars. Then, in 1917, Thomas Wright suggested that there could be many different large star clusters. A few years later, this was proven by other astronomers, and the idea of a galaxy became a reality.
Milky Way
We live in a galaxy called the Milky Way. The Milky Way is part of a cluster of about 3,000 galaxies known as the Local Group. The Milky Way is a spiral galaxy and has an estimated 300 billion stars.
Types of Galaxies
There are four main types of galaxies based on their shape:
Spiral – The Spiral Galaxy has several long arms that rotate around the center. At the center of a spiral galaxy are older stars while the arms are usually made up of new stars.
Barred spiral – This type of galaxy is similar to a spiral but has a long bar in the middle with spirals coming out from the ends.
Elliptical – A mass of stars clustered together in an elliptical disc shape.
Irregular – Any other galaxy shape that is normally classified as irregular. Most irregular galaxies are thought to have formed when two of the other three types of galaxies collide.
Interesting Facts about Galaxies
The word galaxy comes from the Greek word for “milk”.
Some scientists believe that most of the mass of a galaxy is made up of a mysterious substance called dark matter.
It is believed that there is a giant black hole at the center of galaxies.
The closest galaxy to the Milky Way is Andromeda, located about 2.6 million light-years away.
Many galaxies are more than 100,000 light-years away.
It takes more than two hundred million years for the sun to orbit the center of the galaxy. This is called a galactic year.