Dark matter is one of the most mysterious things in the universe. Scientists don't completely understand it yet. They think that dark matter occurs everywhere in the universe. It supposedly is in the space between objects like planets and stars. It cannot be seen, but when observing the night sky, scientists have found large halos, or rings, of what they think is dark matter, surrounding galaxies and galaxy clusters.
Scientists don't know exactly what dark matter is made of. However, scientists have a vague idea about it's content. Here is a list of the theorized content of dark matter: