What is the Universe made of?

Credit: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)

There is more to the Universe than meets the eye. Most of the mass/energy content of the cosmos consists of gravitating dark matter and expansion-accelerating dark energy.The true nature of each component remains a mystery.

Dark matter map. By studying gravitational lensing, astronomers have been able to map the distribution of dark matter in remote clusters of galaxies.
Credit: Kilo-Degree Survey Collaboration/A. Tudorica & C. Heymans/ESO

The Universe consists of hydrogen (75 %), helium (24 %) and a tiny smattering of heavier elements (1 %). However, the elements that we are familiar with are just part of the story. Both theory and observations indicate that the Universe contains huge amounts of dark matter; no one knows what it’s made of. Moreover, empty space appears to be filled with a dark energy that currently accelerates the expansion of the Universe. In all honesty, cosmologists do not know what most of the Universe is made of.

Only 10 % of an iceberg is above sea level. In the Universe, something similar is true: the stars and galaxies that we see make up just a few percent of all there is. No one really understands what the rest is made of.