In 1970 he earned a dr. philos. at the Institute of Theoretical Astrophysics, University of Oslo. Later that year he became professor in astrophysics at the Hamburg Observatory in Germany, and remained in that position until he retired in 2001.
In 1964 and 1966 he published a series of articles on the effects and possible applications of gravitational lenses. He is particularly known for the "Refsdal Method", which describes how one may estimate the expansion rate of the Universe (Hubble constant) using the measured time-delay and lens properties of a gravitationally lensed quasar (QSO). He later started work on stellar evolution, but returned to gravitational lensing shortly before the first detection of a gravitational lens, dubbed the Twin Quasar.
He was a member of the Norwegian Academy of Science and Emeritus at the Institute for theoretical Astrophysics at the University of Oslo. On 1 February 2005 he was awarded the King's Medal of Merit in gold.
- Obituary, Hamburg Observatory
- P. Schneider, J. Ehlers, E.E. Falco, Gravitational Lenses, Springer-Verlag, Berlin 1999. Chapter The period 1963-1979 at Google Books
- Obituary, Institutt for Teoretisk Astrofysikk, 2. February 2009
- Kelly et al., "Multiple Images of a Highly Magnified Supernova Formed by an Early-Type Cluster Galaxy Lens", arXiv:1411.6009.
- Overbye, Dennis (March 5, 2015). "Astronomers Observe Supernova and Find They’re Watching Reruns". New York Times. Retrieved March 5, 2015.
|Recipient of the Fridtjof Nansen Excellent Research Award in Science
(with Jon Storm-Mathisen)