Allan Rex Sandage [1] [2][3][4] was an American astronomer. He was Staff Member Emeritus with the Carnegie Observatories in Pasadena, California.[5] He is best known for determining the first reasonably accurate value for the Hubble constant and the age of the universe.(born June 18, 1926 in Iowa City, Iowa, died November 13, 2010) |
Career
Allan R. Sandage was one of the most influential astronomers of the 20th century.[6] Sandage graduated from the University of Illinois in 1948. By 1953 he earned his Ph.D. from the California Institute of Technology with the German observational astronomer Walter Baade as his advisor. During this time Sandage was a graduate student assistant to the famed cosmologist Edwin Hubble. Sandage continued Hubble's research program after Hubble's sudden death in 1953. Walter Baade's 1952 discovery of two separate populations of Cepheid variable stars in the Andromeda Galaxy, resulted in a doubling of the age of the Universe from 1.8 to 3.6 billion years, since Hubble had only considered the weaker Population II Cepheid variables as standard candles. Following this, Sandage showed that astronomers' previous assumption that the brightest stars in galaxies were of approximately equal inherent intensity was mistaken in the case of H II regions which he found not to be stars and inherently brighter than the brightest stars in distant galaxies. This resulted in another 1.5 factor increase in the age of the Universe, to approximately 5.5 billion years[7]. Throughout the 1950s and well into the 1980s Sandage was regarded as the pre-eminent observational cosmologist. Sandage made seminal contributions to all aspects of the cosmological distance scale from local calibrators within our own Milky Way Galaxy to cosmologically distant galaxies.Sandage began working at the Palomar Observatory. In 1958 he published[8] the first good estimate for the Hubble constant, revising Hubble's value of 250 down to 75 km/s/Mpc, which is quite close to today's accepted value. Later he became the chief advocate of an even lower value, around 50, corresponding to a Hubble age of around 20 billion years.
He performed photometric studies of globular clusters, and deduced that they had an age of at least 25 billion years. This led him to speculate that the Universe did not merely expand, but actually expanded and contracted with a period of 80 billion years. The current cosmological estimates of the age of the universe, in contrast, are typically of the order of 14 billion years. As part of his studies on the formation of galaxies in the early Universe, he co-wrote the seminal paper[9] now called ELS after the authors Olin J. Eggen, Donald Lynden-Bell, and Sandage first describing the collapse of a proto-galactic gas cloud into our present Milky Way Galaxy.
In his paper of 1961 "The Ability of the 200-inch Telescope to Discriminate Between Selected World Models,"[10] he discussed the future of observational cosmology as the search for two parameters - the Hubble constant H0 and the deceleration parameter q0. This paper influenced observational cosmology for at least three decades as it carefully laid out the types of observational tests that could be performed with a large telescope. He also published two atlases of galaxies, in 1961[11] and in 1981,[12] based on the Hubble classification scheme.
In 1962[13] studied a possibility of directly measuring the temporal variation of the redshift of extra-galactic sources, an effect later called Sandage–Loeb effect.[14]
He is noted for the discovery in the M82 galaxy of jets erupting from the core. These must have been caused by massive explosions in the core, and the evidence indicated the eruptions had been occurring for at least 1.5 million years.[15]
He was a prolific researcher with over 500 papers. Until his death he continued to be an active researcher at the Carnegie Observatories, still publishing several papers a year.[16]
[edit] Honors
Awards- Helen B. Warner Prize for Astronomy (1957)
- Eddington Medal (1963)
- Gold Medal of the Royal Astronomical Society (1967)
- National Medal of Science (1970)
- Henry Norris Russell Lectureship (1972)
- Elliott Cresson Medal (1973)
- Bruce Medal (1975)
- Crafoord Prize (1991)
- Main-belt asteroid, 9963 Sandage (1992 AN)
[edit] References
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