Allan Sandage (1926–2010) Astronomer Who Measured Expansion Rate of the Universe

COMMENt Obituary Allan Sandage (1926–2010) Astronomer who measured expansion rate of the Universe.

llan Rex Sandage was one of the most to measure very large distances, and led a fostered by Hubble himself, became prevail- prolific and influential astronomers Hubble Space Telescope team to calibrate ing when the stunningly large redshifts of of the second half of the twentieth their luminosity. quasars were discovered in 1963. Sandage’s Acentury. Edwin Hubble and Walter Baade By 1958, Sandage had massively revised work was instrumental in settling the debate both left their scientific papers to him, and Hubble’s estimates of galactic distances, in favour of an expanding Universe. he continued the work of these two giants increasing them by a factor of about 7. From with spectacular results — including the this he determined an expansion rate of the QUIEt DIscovErIEs first good estimates of the Hubble constant Universe, otherwise known as the Hubble Sandage was actively involved in the and the age of the Universe. constant, of about 75 kilometres per second discovery of quasars — enigmatic objects These are his best known achievements, per megaparsec, and an age of the Universe first detected by radio astronomers in but they comprised only a small part of his of around 13 billion years. Today’s best the late 1950s. Sandage provided some publications, which number in excess of 500. estimates are, remarkably, essentially the of their first optical identifications and In 1956, Sandage became a staff member of same — albeit with smaller errors. the first spectrum. He also co-discovered the Mount Wilson and Palomar observa- radio-quiet quasars, and showed that these tories in California; his retirement almost objects greatly outnumber their radio-loud 50 years later did not stop him from working counterparts. In 1963, he co-wrote a paper until the very end — his last paper is still in on violent processes in galactic centres that the press. He died, aged 84, on 13 November anticipated today’s explanation of quasars as 2010 at his home in San Gabriel, California, being very distant galactic nuclei powered from pancreatic cancer. He is survived by his by black holes. BELLO/SPL F. OF ESTATE caring astronomer wife Mary Sandage and Sandage’s most cited paper is from 1962, his two sons David and John. in which he theorized how the pancake- Sandage was born on 18 June 1926 in Iowa shaped Milky Way was formed by the City, Iowa, as the only child of a powerful collapse of a spherical gas cloud. This work father — a professor of advertising — and remains the basis of modern theories of loving mother. He received his BA in 1948 galaxy formation. from the University of Illinois at Urbana– Sandage also authored several essays on Champaign and then moved to the California the history of modern astronomy, including Institute of Technology in Pasadena, Califor- a monumental history of the Mount Wilson nia, for his PhD. Here he became Hubble’s Observatory. assistant in 1952, a year before completing In mid-career, Allan became deeply con- his degree and Hubble’s sudden death. He cerned about the meaning of life. He studied chose Baade as his thesis adviser, and Baade the Bible and spoke in public about science went on to teach him all the intricacies of the and religion as “two separate closets in the observing techniques of the time. This made same house’’. In the end he highly valued Sandage, who spent roughly 2,000 nights at Christian philosophy, but did not find faith. the telescope during his lifetime, an outstand- He resolved to work to the limit of exhaustion. ing observer. He published the famous book Some people thought that he was ambi- The Hubble Atlas of Galaxies, followed by a Perhaps his seminal work was his 1961 tious, but his drive came from his conviction further two colossal atlases containing some paper ‘The ability of the 200-inch telescope that work was the only meaningful human of the best ground-based pictures of galaxies to discriminate between selected world activity. For Allan, life was not about fun. ever taken. models’, which has become the basis of Allan sometimes called himself a modern observational cosmology. In it, curmudgeon. But in his social life he was EXPANDING thE UNIvErsE Sandage calculated what the past and future radiant with charm and wit; his after-dinner From the very beginning of his career, would look like under different models of talks could make his audience explode with Sandage was a star. His 1953 PhD thesis an expanding Universe and predicted the laughter. He loved books and was a fan of reversed the thinking of the day that faint consequences for an observer. opera. His favourite time was sitting at the ‘main sequence’ stars started their lives as red On the back of these predictions, Sandage dark telescope, as he did for so many nights giants; his measurements of the M3 globular single-handedly mounted a giant programme of his life, taking long exposures while the cluster led to the conclusion that the oppo- to extend the Hubble diagram, which charts dome reverberated with the music of com- site order was correct. This was a revolution redshifts of galaxies (a measure of how fast poser Richard Wagner. ■ in the understanding of stellar evolution. they are moving away from Earth) against Sandage continued to work on determining their relative distances. This became the Gustav A. Tammann is professor emeritus the distances and ages of clusters, as well as crucial piece of evidence that helped to dis- at the University of Basel, CH-4003 Basel, on the properties of their variable stars — the pel doubts about whether very large redshifts Switzerland, and was a co-author of Allan RR Lyrae and Cepheid stars — all his life. are really caused by cosmic expansion, or by Sandage for almost 50 years. He was one of the first to use supernovae some as-yet-unknown physics. Such doubts, e-mail: [email protected]