Such groups exist at different levels:* Star clusters
* Galaxies
* Galaxy clusters
* Superclusters
Galaxy
A galaxy
That is a galaxy.
A group of stars, dust and gases held together by gravity IS CALLED GALAXY
Because of gravity. Only gravity can pull large clouds together with enough force to overcome gas pressure.
New stars together are called a star cluster.They usually travel in space together, for there gravity keeps them in a group.
Gravity
gravity
Many stars together can make up a galaxy. Depending on the arrangement of the stars, they could either make up an elliptical, spiral, barred spiral, lenticular, or irregular galaxy. Stars can also be together by gravity in clusters. Stars that are clustered together in a spherical group are called globular clusters. Many stars are binary stars, meaning that 2 stars circle around either each other, or around a central point of gravity. These are the most basic star groupings in which there are "many" stars.
The answer is simple: gravity.
A collective noun for a group of stars is a cluster of stars (small group) and a galaxy of stars (large group).
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.