OBITUARY John Norris Bahcall 1935–2005 Nuclear Astrophysicist Who Uncovered the Solar Neutrino Problem

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NATURE|Vol 437|1 September 2005 NEWS & VIEWS

OBITUARY John Norris Bahcall 1935–2005 Nuclear astrophysicist who uncovered the solar neutrino problem.

The philosopher Sir Isaiah Berlin once by a cluster of stars is still called the Bahcall– famously quoted a scrap of Archilochus: “The Wolf model; the most widely quoted model fox knows many things, but the hedgehog for our Galaxy was for decades the Bahcall– knows one big thing.” Astrophysicist John Soneira model; and the most accurate models Bahcall would often introduce himself and for the solar interior were those developed a colleague to a new acquaintance with the by Bahcall, with Roger Ulrich, Marc Pinson- sentence: “I know all about neutrinos, and neault and others. my friend here knows about everything else After completing his graduate education at in astrophysics.” Harvard in 1961 (having started his university Such light-hearted self-deprecation was education at Louisiana State University on a typical of Bahcall, who died on 17 August tennis scholarship), he arrived at the Califor- 2005. But it was inaccurate: Bahcall’s scientific nia Institute of Technology (Caltech), working interests and expertise ranged from neutrino with Willy Fowler and others at the time and physics and the structure of the Sun and other place that ‘nuclear astrophysics’ was invented. stars, to galaxy models, quasars and the inter- There he became engaged with neutrino work galactic medium. His more than 600 scientific and to Neta Assaf (then completing her PhD at publications, on an enormous array of sub- Caltech) — the two constant loves of his life. jects, received nearly 20,000 citations. Many His first paper from Caltech, a one-page letter established fundamental paradigms in their to the editor of the Astrophysical Journal, dated fields, and others provided the clearest and 1 December 1962 and entitled “The Solar most comprehensive overview of them. Neutrino Flux” (authored with Fowler, Icko But Bahcall did, in fact, continually return Iben and Richard Sears), proposed an experi- to one core scientific issue: the solar neutrino ment that might “provide a valuable experi- problem. He realized very early in his career mental limit on the effective temperature for the team that produced the 1990 National that we should be able to detect the flux, or neutrino generation in the sun”. That paper set Research Council ‘Bahcall Report’ that set the

stream, of these shadowy fundamental parti- the course for a lifetime of research. scientific and instrumental priorities for astro- C. MOORE cles as they pass through the Earth after escap- The writing of scientific papers was, how- physics in the United States for a decade, and ing from the centre of the Sun, where they are ever, only one of Bahcall’s many contributions worked (with Lyman Spitzer Jr) with tireless produced in prodigious numbers. He clearly to world science. He was an educator who effectiveness in public and in private to have saw that a definite detection, or non-detection, changed the nature of postdoctoral training, the Hubble Space Telescope and the Space of these neutrinos would have major implica- and a scientific statesman of unusual and Telescope Science Institute (STScI) built and tions both for understanding the Sun and for beneficent influence. Bahcall moved to the maintained as one of the world’s pre-eminent fundamental particle physics. For decades, he Institute for Advanced Study (IAS) at Prince- scientific facilities. encouraged and supported scientists through- ton in 1968 and soon established that institu- Neta Bahcall, a distinguished scientist out the world in studying this problem and tion as a magnet and model for postdoctoral herself, was his love, his best friend and his was most successful in his collaboration with training. A significant fraction of the world’s scientific colleague throughout. She took Raymond Davis Jr, who ultimately won the most distinguished astrophysicists benefited a leading scientific role at the STScI and Nobel Prize in 2002 for detecting the solar from his tutelage and the intellectually fertile wrote over 30 papers with him on subjects neutrino flux. atmosphere that he established there. The ranging from solar neutrinos to binary X-ray It was Bahcall’s persistent work that proved eminent British scientist Sir Martin Rees sources. They also collaborated in raising definitively that the low flux found by the solar describes himself as fortunate to have been one three talented children, Safi, Dan and Orli, neutrino experiments of Davis and others of the first IAS postdoctoral fellows in astro- who are themselves now establishing signifi- could not be explained by errors in our model physics in 1969. The birthdays of all the fellows cant scientific careers. for the Sun. Neutrinos seemed to be missing: and important family events were celebrated. But no listing of achievements can con- either they were not made at the rates required The intellectual atmosphere was intense, and vey the impression of the man: the wit, by standard nuclear physics, or they were the weekly Tuesday lunches, with John presid- the mischievous energy, the passion. Jerry made but then somehow ‘lost’ in transit ing, to which the whole Princeton physics Wasserburg, his old Caltech friend, portrays between the Sun and the Earth. The latter community was invited, were legendary. Bah- Bahcall in 1965: “John, running around in explanation — neutrino mixing, in which one call’s postdoc programme was the one that white tennis shorts, very sportive and com- type of neutrino changes into another at some astrophysics institutions worldwide emulated. petitive in both creative science and tennis, rate, and in which the neutrino must have a At the IAS, young scientists were selected and trying out and enthusiastically arguing every small but finite mass — is now known to be recruited in the most exacting manner and new idea in astrophysics; he was the dynamo true, and it is surely due to Bahcall’s tenacity then were free to work on whatever they of the institute.” ■ and insight that this important and surprising wanted, with whomever they wished. Jeremiah P. Ostriker modification to the standard model of particle While maintaining a scientific and educa- Jeremiah P. Ostriker is in the Department of physics was uncovered. tional programme that would have exhausted Astrophysical Sciences, Princeton University, A fuller idea of his exceptional scientific most, Bahcall also demonstrated extraordi- Peyton Hall, Ivy Lane, Princeton, New Jersey scope is indicated by the fact that the standard nary scientific leadership. He was president of 08544-1001, USA. model for a massive black hole surrounded the American Astronomical Association, led e-mail: [email protected]