Notes

Dark matter, constituting 30.1 percent of the universe's matter-energy makeup, remains hidden from sight, detectable only by its gravitational influence. Originally termed the "missing mass," its existence was first deduced by astronomer Fritz Zwicky in 1933 when he realized that the stars in the Coma cluster didn't supply enough mass to hold the galaxies together. Confirmation came in the 1970s from Vera Rubin and W. Kent Ford's observation that galaxies rotate as if they contain more mass than visible stars suggest. This unseen mass, dubbed dark matter, remains invisible but affects galactic motions. Gravitational lensing and observations like those in the Bullet cluster reveal dark matter's presence. While some dark matter might consist of familiar baryons, most is nonbaryonic and "cold," comprising particles called weakly interacting massive particles (WIMPs). These particles, not accounted for in the standard model of particle physics, are actively sought through various experiments. Proposed modifications to gravity struggle to explain the observed effects of dark matter.


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