Fritz Zwicky (1898-1974), Swiss-US astronomer. He spent most of his early life in Switzerland, before moving to the USA in 1925. His major work was on supernovae, stars which brighten an enormous amount in an explosive death. He started looking for supernovae in 1936, intending to find out how anything could appear so bright at distances of millions of light years. He showed that they are up to 100 million times brighter than the Sun. Along with Walter Baade, he suggested that a neutron star may be formed at the heart of a supernova, a theory still accepted in stellar evolution.