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Understanding Dark Matter and Dark Energy

It may come as a surprise that visible matter only constitutes 4 percent of the universe’s contents. The other 96% is made of what we refer to as dark matter and dark energy. While scientists were able to discover both by observing their effects in the cosmos, neither has actually been directly detected. The wonders and mysteries of the dark universe continue to be explored at Fermilab.

A matter of something else at work

Dark matter was discovered by scientists who studied how nearby galaxies and galaxy clusters behave. Some of these behaviors couldn’t be explained by the visible matter that was present. The scientists inferred that there had to be other entities present that were adding to galaxies’ mass and creating a gravitational pull. These undetectable other ‘things’ were named dark matter.

Greater than gravity

Similar to dark matter, dark energy is a concept that was formulated to answer a question—in this case, about the universe’s expansion. It was understood that after the big bang, the universe is expanding. At the same time, the gravitational forces generated by all of the matter in the universe should have slowed that expansion to some degree. Yet scientists have learned that the universe is actually expanding at an increasing rate. This strongly suggests that there is a force in the universe that is overpowering gravity—a force we call dark energy.

Seeing the dark more clearly

In the early 80s, scientists at Fermilab were among the first to link the fields of astrophysics and particle physics to create the field of particle astrophysics, to include the study of dark matter and dark energy. In 1983, Fermilab formed a team of physicists, postdocs, and students to create the first Theoretical Astrophysics Group, which has since developed over 1,000 published papers. By the end of the decade, Fermilab was actively testing astrophysics theories by participating in projects such as the Sloan Digital Sky Survey, the Cryogenic Dark Matter Search experiment and the Pierre Auger Observatory.

Fermilab scientists are continuing to explore this still largely unknown frontier today. Learn more about dark matter and energy.

Photo credit (above): Dark Energy Survey, Dark Energy Camera, Cerro Tololo Observatory, Chile Photo, Reidar Hahn,Fermilab

Fermilab Building