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A system of billions of stars held together by gravity is called a galaxy. The one we live in is called the Milky Way galaxy.
gravity
Stars are balls of (usually hydrogenous) gas that is held together by a large amount of gravity. The gravity squeezes the gases together causing the star to become very hot and also causes nuclear fusion. The sun is the largest star but luckily earth is far enough away that the gravity of the sun doesn't pull us into it.
Gravity keeps the planets in orbit around the sun and the stars and the stars in orbit around the center of the galaxy. Gravity also holds the stars together against their own internal pressure.
An island comprising billions of stars and nebulae, held together by gravity.
A system of billions of stars held together by gravity is called a galaxy. The one we live in is called the Milky Way galaxy.
a cluster
Galaxy
Exactly, that is what a galaxy is.
That is a galaxy.
Is called a galaxy
Gravity.
Because of gravity. Only gravity can pull large clouds together with enough force to overcome gas pressure.
Gravity
gravity
The answer is simple: gravity.
Stars are balls of (usually hydrogenous) gas that is held together by a large amount of gravity. The gravity squeezes the gases together causing the star to become very hot and also causes nuclear fusion. The sun is the largest star but luckily earth is far enough away that the gravity of the sun doesn't pull us into it.