Galaxies and their formation

The MilkyWay formed from dust and gas from the big bang. Gravity then collected the dust and gas.  The gas forms millions of stars. The gravity gets so strong towards the center of the galaxy and creates a supermassive black hole that causes the stars to spin around the galaxy. That's how the MilkyWay, and other whirlpool galaxies form. Some don't get there black hole and are less organized. Each galaxy holds thousand to trillions, of stars. And there are millions of galaxies. Are galaxy has a close enemy that will eventually bash into the MilkyWay causing the two galaxies to charge at each other many times. Then will make a huge galaxy.