A GALAXY IS A HUGE MASS OF STARS , nebulae, and interstellar material .The smallest Galaxies contain about 100,000 stars , while the largest contain up to 3,000 billion stars . There are three main types of Galaxy , classified according to their shape ;elliptical ,which are oval shaped; spiral, which have arms spiraling outwards from a central bulge; and irregular, which have no obvious shape .Some times , the shape of a galaxy is distorted by by a collision with another galaxy .Quasars (quasi -stellar objects ) are thought to be galactic nuclei but are so far away that their exact nature is still uncertain.They are compact ,highly luminous objects in the outer reaches of the known Universe . while the furthest known " ordinary" Galaxies are about 10 billion light years away , the furthest known quasar is about 1