1. Landau, L.: Phys. Z. Soviet 1, 285 (1932).
2. Chandrasekhar, S.: Phil. Mag. 7, 63 (1929). Also Monthly Notices Roy. Astron. Soc. 91, 456 (1931).
3. Baade, W. and Zwicky, F.: Phys. Rev. 45, 138 (1934).
4. Staelin, D. H. and Reifenstein, E. C.: Science
162, 1481 (1968).
5. For a detailed account see e.g. Shklovski, J. S.: Supernovae, New York, 1968.