Dark matter is very different from the ordinary matter we see and interact with every day. Dark matter interacts very weakly or almost not at all with the ordinary matter that we and our measuring instruments are made of. The exception is that dark matter does exert gravitational attraction, just like ordinary matter. Isaac Newton demonstrated in 1687 that matter attracts all other matter in the universe with the force of gravity.
Astronomers have studied gravitational forces in the universe at all distance scales (from the rotation of stars in galaxies, to the motion of galaxies in clusters, to the structure of the cosmos since the Big Bang) for nearly a century. Surprisingly, the measured gravity far exceeds (by about five times) what can be explained by ordinary matter. Basically, there’s not enough ordinary matter in the universe to explain why galaxies stay together or how they formed in the first place.
The term dark matter was coined in 1933 by Fritz Zwicky of the California Institute of Technology to describe the unseen matter needed to explain the fast-moving galaxies in the Coma Cluster. In the 1970s, Vera Rubin of the Carnegie Institution found evidence for dark matter in her research on galaxy rotation. Today we have much more evidence for the presence of dark matter in galaxies, the interaction of dark matter halos during galactic cluster collisions, and the distribution of dark matter (and even its absence) across different types of galaxies.
Scientists have overwhelming indirect evidence for dark matter. However, its nature remains a mystery. Alternative theoretical explanations for the effects of dark matter, such as modifications to the theory of gravity, don’t fit with observational evidence. Similarly, scientists’ astronomical searches have failed to find evidence to support models suggesting that the missing matter could be in compact objects of ordinary matter.
Scientific evidence points to dark matter being a new type of fundamental particle or particles that interact with ordinary matter through gravity. Scientists have several candidates for the types of particles that make up dark matter. One possibility is that dark matter is made of WIMPs (weakly interacting massive particles) that would have 1 to 1,000 times more mass than a proton. Another candidate is the axion, a particle with ten-trillionth of the mass of an electron. In theory, axions would convert to a particle of detectable light (called a photon) in the presence of strong magnetic fields. Alternately, dark matter may exist in a rich and complex set of particles that would form a universe parallel to our own (the so-called Dark Sector).
DOE Office of Science: Contributions to Dark Matter
The Department of Energy (DOE) Office of Science High Energy Physics program supports research on dark matter through leading-edge experiments, including some in partnership with the National Science Foundation and NASA. Researchers use large, sensitive detectors located deep underground to directly search for the dark matter particles that may continually pass through the Earth. Researchers can also search for dark matter indirectly through specific signatures in cosmic rays and gamma rays. Scientists search for these signatures using ground-based and space-based observatories. Researchers are also trying to create dark matter with particle accelerators, such as the Large Hadron Collider and various DOE Office of Science user facilities.
Dark Matter Facts
- Dark matter makes up about 85 percent of the total matter in the universe, accounting for more than five times as much as all ordinary matter.
- Dark matter played an important role in the formation of galaxies and the evolution of the universe.
- Dark matter remains strange and illusive but tremendously important to our understanding of nature, from the most fundamental particles to origins and evolution of the universe.
- Decades of search for dark matter have yielded great scientific and technological advances, including developments in new materials, hypersensitive sensors, cryogenics and superconductivity, and algorithms for high-performance supercomputers, quantum computers, and artificial intelligence.
Resources and Related Terms
- Office of High Energy Physics
- Physics at the National Science Foundation
- DOE’s Direct Current podcast, A Shot in the Dark
- The Search for Dark Matter
- Cosmic Ray Tool Repaired in Space
- Science Highlight: Hunting for Sterile Neutrinos with Quantum Sensors
- Science Highlight: Discovery of Low-lying Isomeric States in Cesium-136 Has Applications in Particle Astrophysics
- Detecting Dark Matter with Quantum Computing
- A Quantum Sense for Dark Matter
Acknowledgements
Manuel Bautista (DOE)
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