Zwicky, Fritz (1898-1974)

Swiss astronomer. He predicted the existence of neutron stars in 1934. He discovered 18 supernovae and determined that cosmic rays originate in them.

Zwicky observed that most galaxies occur in clusters, each of which contains several thousand galaxies. He made spectroscopic studies of the Virgo and Coma Berenices clusters and calculated that the distribution of galaxies in the Coma Berenices cluster was statistically similar to the distribution of molecules in a gas when its temperature is at equilibrium. Beginning 1936, he compiled a catalogue of galaxies and galaxy clusters in which he listed 10,000 clusters.

Zwicky was born in Varna, Bulgaria, but his parents were Swiss and he retained his Swiss nationality throughout his life. He studied at the Federal Institute of Technology in Zürich, gaining a BA and then a PhD by 1922, then moved to the USA 1925 to work as a theoretical physicist at the California Institute of Technology, Pasadena. He was appointed assistant professor in 1927 and professor of astrophysics in 1942, and remained there until his retirement in 1968.

Zwicky was among the first to suggest that there is a relationship between supernovae and neutron stars. He suggested in the early 1930s that the outer layers of a star that explodes as a supernova leave a core that collapses upon itself as a result of gravitational forces.