Searle, Leonard T.

Leonard Searle’s most enduring contribution to astronomy is his 1978 model, with Robert Zinn, for how the Milky Way galaxy formed. With Wallace Sargent, he studied the helium abundance in the early universe, using horizontal branch stars and compact young galaxies. In the process, they developed the “simple model” of chemical evolution in galaxies, a formalism used by astronomers today. As Director of Carnegie Observatories (1989–1996), he helped usher in the era of big-telescope astronomy.