Answer:
the objects in the universe are evenly placed. This means that a celestial object's gravity may not be able to attract another object. Another reason may be that the stars in solar systems act as points of equilibrium for the planets in the system. Take for example the sun. It maintains the position of the planets in the system and likewise the earth maintains the position of the moon. You can picture it as evenly placed atoms in matter and the subsequent electrons held by the nucleus