February 8: Fritz Zwicky

Fritz Zwicky

February 14, 1898 – February 8, 1974

Fritz Zwicky was a Bulgarian born, America-based Swiss astronomer. He was an original thinker, with many important contributions in theoretical and observational astronomy. His amazing scientific career is relatively unknown to the general public, but he remains a giant in the astronomical community.

He was responsible for positing numerous cosmological theories that have a profound impact on understanding of our universe today. He was appointed Professor of Astronomy at Caltech in 1942 and also worked as a research director/consultant for Aerojet Engineering Corporation (1943-1961) and staff member of Mount Wilson Observatory and Palomar Observatory for most of his career.

In an article titled “Idea Man” published in 2001 Stephen M. Maurer wrote that Zwicky will be “remembered as a gifted observational astronomer who had discovered more supernovae than everyone else in human history combined. Today, Zwicky’s reputation is bigger than ever, except that now astronomers think of him as a theorist. When researchers talk about neutron stars, dark matter, and gravitational lenses, they all start the same way: ‘Zwicky noticed this problem in the 1930s. Back then, nobody listened . . .’”

Together with colleague Walter Baade, Zwicky pioneered and promoted the use of the first Schmidt telescopes used in a mountain-top observatory in 1935. He hand-carried the Schmidt lens from Germany, which had been polished by the optician, Bernard Schmidt. In 1934 he and Baade coined the term "supernova" and hypothesized that they were the transition of normal stars into neutron stars, as well as the origin of cosmic rays. It was a prescient insight that had tremendous impact in determining the size and age of the universe in subsequent decades.

In support of this hypothesis, Zwicky started hunting for supernovae, and found a total of 120 by himself over a stretch of 52 years, a record which still stands as of 2006 (the current runner-up is Jean Mueller, with 98 discoveries and 9 co-discoveries).

While examining the Coma galaxy cluster in 1933, Zwicky was the first to use the virial theorem to infer the existence of unseen matter, what is now called dark matter. He was able to infer the average mass of galaxies within the cluster, and obtained a value about 160 times greater than expected from their luminosity, and proposed that most of the matter was dark. The same calculation today shows a smaller factor, based on greater values for the mass of luminous material; but it is still clear that the great majority of matter is dark.

Zwicky devoted considerable time to the search for galaxies and the production of catalogs. From 1961 to 1968 he and his colleagues published a comprehensive six volume Catalogue of galaxies and of clusters of galaxies. They were all published in Pasadena, by the California Institute of Techology.

In 1949, Truman awarded Zwicky the Presidential Medal of Freedom, for work on rocket propulsion during World War II. In 1968, Zwicky was made professor emeritus at California Institute of Technology. In 1972, Zwicky was awarded the Gold Medal of the Royal Astronomical Society, their most prestigious award, for "distinguished contributions to astronomy and cosmology". This award noted in particular his work on neutron stars, dark matter, and cataloging of galaxies. The asteroid 1803 Zwicky and the Lunar crater Zwicky are both named in his honour.