The same thing that keeps the Solar System from moving apart, and that keeps the Moon in orbit around Earth: gravity. In the case of galaxies, usually at least 80% of the gravity is from invisible dark matter.
Hundreds of billions of stars, some of them with planets.
we are in the milky way galaxy
The center of the elliptical galaxy is very dense with many stars, and density decreases farther out.
the purpose is the gravitational pull wich keeps the planets and stars from drifting apart
If you mean by more stars being created in it, then yes. If you mean that the stars in it move apart (as in, away from the centre), then no. Our galaxy is continiously moving away from other galaxys, which has got alot to do with the 'big bang'. So to answer your question, you're going to have to make your own options because your question is too vague.
There aren't any, to access the trial galaxys, you must collect 3 green stars.
outer stars
Stars (apart from our Sun) are not a part of our Solar System.Stars (apart from our Sun) are not a part of our Solar System.Stars (apart from our Sun) are not a part of our Solar System.Stars (apart from our Sun) are not a part of our Solar System.
Gravity keeps them that way.Gravity keeps them that way.Gravity keeps them that way.Gravity keeps them that way.
the stonecutters
because the stars apart of the solar system.
Old Glory is commonly used as well.