Allan Sandage | |
|---|---|
 Sandage in 1981 | |
| Born | (1926-06-18)June 18, 1926 |
| Died | November 13, 2010(2010-11-13) (aged 84) |
| Alma mater | California Institute of Technology University of Illinois |
| Known for | Physical cosmology |
| Awards | Helen B. Warner Prize for Astronomy(1957) Eddington Medal(1963) Rittenhouse Medal(1968) National Medal of Science(1970) Elliott Cresson Medal(1973) Bruce Medal(1975) Crafoord Prize(1991) Fellow of the Royal Society[1] |
| Scientific career | |
| Fields | astronomy |
| Institutions | Carnegie Observatories |
| Doctoral advisor | Walter Baade |
Allan Rex Sandage (June 18, 1926 – November 13, 2010) was an Americanastronomer. He was Staff MemberEmeritus with theCarnegie Observatories inPasadena, California.[2] He determined the first reasonably accurate values for theHubble constant and theage of the universe.
| (96155) 1973 HA | 27 April 1973 |
Sandage was one of the most influential astronomers of the 20th century.[3] He was born inIowa City, Iowa,United States. He graduated from theUniversity of Illinois in 1948. In 1953 he received aPhD from theCalifornia Institute of Technology; theGerman-born Wilson Observatory-based astronomerWalter Baade was his advisor. During this time Sandage was a graduate student assistant to cosmologistEdwin Hubble. He continued Hubble's research program after Hubble died in 1953.
In 1952 Baade surprised his fellow astronomers by announcing (at the 1952 Conference of theInternational Astronomical Union, in Rome) his determination of two separate populations ofCepheid variable stars in theAndromeda Galaxy, resulted in a doubling of the estimatedage of the universe (from 1.8 to 3.6 billion years). Hubble had posited the earlier value; he had considered only the weaker Population II Cepheid variables asstandard candles. After Baade's pronouncements, Sandage showed that astronomers' previous assumption, that the brightest stars in galaxies were of approximately equal inherent intensity, was mistaken in the case ofH 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-fold increase in the calculated age of the universe, to approximately 5.5 billion years.[4]
Throughout the 1950s and well into the 1980s Sandage was regarded as the pre-eminent observationalcosmologist, making contributions to all aspects of the cosmological distance scale, ranging from calibrators within our ownMilky Way Galaxy, to cosmologically distant galaxies.
Sandage began working at thePalomar Observatory. In 1958 he published[5] the first good estimate for theHubble constant, revising Hubble's value of 250 down to 75 km/s/Mpc, which is close to today's accepted value. Later he became the chief advocate of an even lower value, around 50, corresponding to aHubble age of around 20 billion years. At the time, many, especially Sandage, believed that thecosmological constant was zero. In such a case, a low Hubble constant is necessary in order for the age of the universe (as opposed to theHubble age) to be at least as old as the oldest objects it contains, i.e. ca. 14 billion years.
Sandage performed photometric studies ofglobular clusters, and calculated their age to be 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 concerning the formation of galaxies in the early universe, he co-wrote the paper[6] now referred to as ELS after the authorsOlin J. Eggen,Donald Lynden-Bell and Sandage, first describing the collapse of a proto-galactic gas cloud into our present Milky Way Galaxy. He later defended the paper in 1990.[7]
In his 1961 paper "The Ability of the 200-inch Telescope to Discriminate Between Selected World Models,"[8] he suggested that the future of observational cosmology would be the search for two parameters: theHubble constant H0 and thedeceleration parameter q0. This paper influenced observational cosmology for at least three decades as it carefully specified the types of observational tests that could be performed with a large telescope. He also published two atlases of galaxies, in 1961[9] and 1981,[10] based on theHubble classification scheme.
In 1962 Sandage studied the possibility of directly measuring the temporal variation of the redshift of extra-galactic sources.[11] This analysis became known as the "Sandage–Loeb test".[12]
Sandage discovered jets erupting from the core of the so-calledCigar Galaxy. These must have been caused by massive explosions in the core, and they have apparently been occurring for at least 1.5 million years.[13]
Sandage was a prolific researcher; during his career he published more than 500 papers. Until his death he continued to be an active researcher at theCarnegie Observatories, still publishing several papers a year.[14]
In 1959, Sandage married Mary Connelley, also an astronomer, with whom he had two sons, David and John.[15] In 1983 Sandage announced he had become aChristian[16] and began to write essays on the subject of religion and science.[17] On November 13, 2010, Sandage died ofpancreatic cancer at his home inSan Gabriel, California. He was 84 years old.[15][18][19][20]
Awards
Named after him
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