Galaxy Formation Pioneer Dr. Leonard Searle Dies

Leonard Searle, astronomer and director emeritus of Carnegie Observatories, died at his home on July 2, 2010, in Pasadena, CA, in the midst of a busy retirement that followed a long, distinguished scientific career.

Searle was born on October 23, 1930, in the London suburb of Mitcham to parents of modest means. He received his Bachelor of Science degree from University of Saint Andrews in Scotland, and his PhD from Princeton University, where he met his future wife, Eleanor Millard. They were married in Princeton in 1952. Eleanor, his lifelong companion, was a distinguished medieval historian who joined the Division of the Humanities and Social Sciences at Caltech as professor in 1979. She died in 1999.

Leonard joined the faculty at University of Toronto in 1953, resigning that position in 1960 to become a Senior Research Fellow at Caltech, where he worked with Jesse Greenstein and Wallace Sargent on the chemical compositions of stars. The Caltech appointment marked the beginning of a fruitful association with Sargent, with whom he published 25 papers. In 1963 Searle left Caltech to join the faculty of the Mount Stromlo Observatory in Australia. Then in 1968 he returned to Pasadena to join the staff of Carnegie Observatories, his final academic home.

Several themes punctuate Searle’s academic career. One of the most persistent was the abundance of helium in the very early universe, a quantity whose numerical value is of great importance for cosmology. He pursued this topic with Sargent, first in the study of old evolved “horizontal branch” stars. Later, convinced that such stars could not provide a satisfactory answer, he and Sargent turned to certain small galaxies which provided more reliable estimates of the important helium-to-hydrogen abundance ratio. In the pursuit of this answer they devised the “simple model” of chemical evolution, a formalism used by astronomers to this day.

He worked with the Dutch astronomer Piet van der Kruit to construct successful models of certain spiral galaxies by careful measurements of surface brightness, and later he worked with colleagues in Pasadena to derive the abundances of chemical elements in primordial stars of our Milky Way Galaxy.

His most successful venture was the formulation of a scheme for the assembly of the Milky Way Galaxy from “primordial fragments.” This work, which he undertook with then-Carnegie Fellow Robert Zinn, has withstood the test of time. It has been quoted more than 1000 times since it was published in 1978.

Searle accepted the Directorship of Carnegie Observatories in 1989 at a signal time in its history. Under his leadership an initial plan to build a single 8.4 meter telescope evolved finally into the construction of two 6.5 meter telescopes, operated since 2000 by a 5-institution consortium at Carnegie’s Las Campanas Observatory in Chile. Searle’s vital contribution to the Magellan project was his shrewd ability to hire good experts, and then to delegate authority in ways that invited their fruitful participation. All the while, Searle managed to maintain the Observatories’ tradition of academic excellence, even as it was plunging into a new world of big-telescope technology. He pursued a visiting scholars program, and he used the important telescope time-allocation process to promote the intellectual growth of Carnegie scientists. His sympathy for the plight of financially strapped Eastern European astronomers took the form of support for the Polish OGLE telescope, to this day a shining success story at Carnegie’s Las Campanas Observatory.

Following retirement in 1996, Searle continued to follow the progress of the Observatories by frequent contact with his colleagues of many years. He and Eleanor wintered in Pasadena, and during hot Pasadena summers they escaped to their home at Somerset in the south of England. Searle maintained an avid interest in both British and American politics.