Why Does The Milky Way Have Arms
A third of our galaxies are a flat spiral with a bulging center. Astronomers think that the reason why galaxies have arms at the end of the spiral is because they rotate. They also believe this because it spins around the bulge in the center of the galaxy or because they have something that looks like a wave called a ¨destiny wave¨. A destiny wave can't move on it's own. Water also doesn´t move on its own. It moves by energy waves instead, and also as energy waves passes the water it affects it. The stars go around the galaxy center. The energy wave cause the stars to slow slightly temporarily and clump together. Astronomers wondered for a long time why the galaxies arms never go away after a couple spins.