Galaxy it is part of the universe where it is made up of many stars, clouds, dust and gas. The solar system made up of planets like the Earth we live in is a small part of the galaxy.
Galaxy comes from the Greek word galaxies which means milk or in English the milky way (milk circle). A galaxy is a large group of stars, gas and dust bound together by gravity, according to the NASA website.
Galaxies are made up of one or more large celestial bodies surrounded by particles. Various types of particles from galaxies include planets, gases, nebulae, stars, dust, and other celestial particles.
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The universe has a large number of galaxies. The existence of these galaxies is scattered throughout the universe with distances and empty spaces between them. Galaxies can be compared to small islands scattered throughout the universe.
The size of the galaxy is very large because it is made up of millions or even billions of stars within it. Between the distance of one galaxy from another galaxy there is a very large space. Empty space also exists between any supercluster or cluster of galaxies.
Galaxy formation theory
In the book Ready to take Rogers Pakpaham et al. 2010 High School / MA National Geography Exam, there are several theories on the formation of galaxies. Here are two theories about its formation galaxy:
1. Fowler’s hypothesis
Fowler’s hypothesis states that about 12 billion years ago, the shape of the galaxy was hydrogen gas that rotated to take on a spherical shape. Hence, the gas undergoes a contraction which produces many stars.
2. The Hubble hypothesis
In this theory it is stated that the galaxy was originally a fog that resembles a ball. The ball rotates so fast that it forms a smooth spiral. Hence, the sphere develops in galaxies from Sba to Sbc.
Types of galaxies
From the same book it is said that galaxies are divided into three types, namely:
1. Spiral galaxy
Of all the galaxies in the universe, about 80% have a spiral shape. This spiral galaxy is made up of three parts, namely the center point, the circle of stars and the rotating stack of stars. When viewed from the side, spiral galaxies are like ellipses with arms and their surroundings are surrounded by an atmosphere with radiant rays.
An example of this spiral galaxy is the Milky Way.
2. Elliptical galaxy
Elliptical galaxies make up about 17% of the total number of galaxies in the universe. It is called an elliptical galaxy because of its large, shiny oval shape. This elliptical galaxy is almost similar to an oval-shaped ball
like a rugby ball.
An example of an elliptical galaxy is Galaxy M87 or a galaxy known for its shape in the constellation Virgo.
3. Irregular galaxy
This irregular galaxy is shaped like a cloud of fog or is similar to a bunch of stars. This galaxy has billions of blue stars.
An example of an irregular galaxy is the Magellanic cloud which is 180,000 light years from Earth galaxy Milky Way.
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