Dark matter

• Stars in galaxies do not reduce in orbital speed as the distance from the center of the galaxy increases, as do the planets in our solar system. This would imply that there is more matter in the galaxy than is visible. This is dark matter.
• Dark matter is required for the formation of galaxies. Clouds of gas are simply not dense enough to produce the required gravity. Computer simulations (cosmologist Carlos Frank) indicate that dark matter amounts around five times that of normal matter will satisfy simulation requirements for a galaxy creation.