In this series I give you an overview of important ideas in the area of cosmology. This video is the second in the series, and focuses on dark matter.
Using various detectors and research methods, astronomers have determined that the stuff we see in space — stars, gas, and dust — amounts to less than 5 percent of the universe. This stuff is ordinary matter, and it's made up of protons, neutrons, and electrons. Scientists call ordinary matter "baryonic matter" because protons and neutrons are subatomic particles called baryons.
So if ordinary matter is only about 5 percent of the universe, what's the other 95 percent? Well, about 23 percent is something called dark matter.