dark energy and dark matter.

NEW YORK — All the stars, planets and galaxies that can be seen today make up just 4 percent of the universe. The other 96 percent is made of stuff astronomers can't see, detect or even comprehend. These mysterious substances are called dark energy and dark matter.

12 May 2011

https://www.space.com/11642-dark-matter-dark-energy-4-percent-universe-panek.html