Sjur Refsdal (30 December 1935 – 29 January 2009) was a

Norwegian Norwegian, Norwayan, or Norsk may refer to: *Something of, from, or related to Norway, a country in northwestern Europe * Norwegians, both a nation and an ethnic group native to Norway * Demographics of Norway *The Norwegian language, including ...

astrophysicist, born in

Oslo Oslo ( , , or ; sma, Oslove) is the capital and most populous city of Norway. It constitutes both a county and a municipality. The municipality of Oslo had a population of in 2022, while the city's greater urban area had a population ...

. He is best known for his pioneer work on

gravitational lensing A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer. This effect is known ...

, including the Chang-Refsdal lens.

Biography

In 1970 he earned a

doctorate A doctorate (from Latin ''docere'', "to teach"), doctor's degree (from Latin ''doctor'', "teacher"), or doctoral degree is an academic degree awarded by universities and some other educational institutions, derived from the ancient formalism ''li ...

at the Institute of Theoretical Astrophysics,

University of Oslo The University of Oslo ( no, Universitetet i Oslo; la, Universitas Osloensis) is a public research university located in Oslo, Norway. It is the highest ranked and oldest university in Norway. It is consistently ranked among the top universit ...

. Later that year he became professor in astrophysics at the

Hamburg Observatory Hamburg Observatory (german: Hamburger Sternwarte) is an astronomical observatory located in the Bergedorf borough of the city of Hamburg in northern Germany. It is owned and operated by the University of Hamburg, Germany since 1968, although i ...

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

, 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 Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving ...

) using the measured time-delay and lens properties of a gravitationally lensed Supernova (SN). This method was applied for the first time in 2018, with the homonymous SN Refsdal. He later started work on stellar evolution, but returned to

shortly before the first detection of a

gravitational lens A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer. This effect is known ...

, dubbed the Twin Quasar. He was a member of the Norwegian Academy of Science and Emeritus at the Institute for theoretical Astrophysics at the

. On 1 February 2005 he was awarded the

King's Medal of Merit The King's Medal of Merit (Norwegian: ''Kongens fortjenstmedalje'') is a Norwegian award. It was instituted in 1908 to reward meritorious achievements in the fields of art, science, business, and public service. It is divided in two classes: gold ...

in gold. The first detected multiply-lensed supernova was nicknamed " SN Refsdal" in his honor.

References

{{DEFAULTSORT:Refsdal, Sjur 1935 births 2009 deaths Scientists from Oslo Norwegian astronomers 20th-century astronomers 21st-century astronomers University of Oslo alumni Norwegian expatriates in Germany Recipients of the King's Medal of Merit in gold Members of the Norwegian Academy of Science and Letters