The discovery of dark matter was not a single event but rather a result of several independent observations and scientific investigations. Here is a summary of the key pieces of evidence and observations that led to the discovery of dark matter:
Gravitational Effects: In the 1930s, Swiss astronomer Fritz Zwicky studied the Coma galaxy cluster and observed that the visible mass of the cluster was insufficient to explain the gravitational forces required to hold it together. He hypothesized the existence of "dark matter" to account for the missing mass.
Galaxy Rotation Curves: In the 1970s, astronomers Vera Rubin and Kent Ford studied the rotation curves of galaxies. They found that the stars in galaxies were moving at velocities that could not be explained by the visible mass alone. The observed velocities indicated the presence of additional mass, which became known as dark matter.
Cosmic Microwave Background (CMB): In the 1990s, precise measurements of the cosmic microwave background radiation were made by experiments such as the Cosmic Background Explorer (COBE) and later the Wilkinson Microwave Anisotropy Probe (WMAP) and the Planck satellite. These measurements provided crucial information about the distribution of matter and energy in the early universe. They indicated that ordinary matter (atoms) accounted for only a small fraction of the total matter-energy content of the universe.
Large-Scale Structure Formation: Observations of the large-scale structure of the universe, including the distribution of galaxies and galaxy clusters, further supported the presence of dark matter. The gravitational effects of dark matter were necessary to explain the observed patterns of clustering and the formation of cosmic structures.
Gravitational Lensing: The phenomenon of gravitational lensing, where the gravitational pull of massive objects distorts the light from more distant objects, has provided additional evidence for dark matter. The gravitational lensing effects observed in galaxy clusters suggest the presence of significant amounts of unseen matter.
It is important to note that although dark matter has been inferred through its gravitational effects, its exact nature and composition remain unknown. Various candidates, such as weakly interacting massive particles (WIMPs), are being investigated, but direct detection and conclusive identification of dark matter particles are still ongoing scientific endeavors.