John N. Bahcall, 70, an astrophysicist who did pioneering work on the fundamental properties of the sun, including how it shines, and who was a leader in the development of the Hubble Space Telescope, died Aug. 17 at New York-Presbyterian/Weill Cornell Hospital in New York City.
According to the Institute for Advanced Study in Princeton, N.J., where he had been a faculty member for more than three decades, he died of a rare blood disorder.
Dr. Bahcall was best known for his 1964 idea that measuring the number and properties of neutrinos arriving on Earth from the sun provided insights into the nature of the sun. Neutrinos, among the elemental particles making up the universe, are produced as byproducts of the nuclear fusion reactions that power stars.
In a 2002 commencement address to physics and astronomy graduates at the University of California at Berkeley, Dr. Bahcall recounted how he and Raymond Davis, a physical chemist, set out in 1961 to determine whether there was a direct way to test the theory of how stars shine. They were looking for a way to observe the neutrinos produced deep inside the sun as hydrogen is burned to helium.
Using neutrinos to look inside the sun was analogous, Dr. Bahcall told the graduates, to a doctor using ultrasound or X-rays to look inside human bodies. Their work did, indeed, offer insights into solar physics.
In 1968, Davis set up an experiment to catch neutrinos in a tank filled with cleaning fluid in a South Dakota gold mine. He found a discrepancy between Dr. Bahcall's predictions and the number of neutrinos he actually captured, which came to be known as the "solar neutrino problem." Efforts to resolve that discrepancy over the years led to the conclusion that neutrinos change shape, which is why they eluded detection in South Dakota.
In the 1970s, Dr. Bahcall, together with Princeton astronomer Lyman Spitzer Jr., led the effort to create the Hubble telescope, which was launched in 1990. He chaired the National Academy of Sciences committee that created the decade-long plan for U.S. astronomy research, which came to be known as the Bahcall Report.
A passionate Hubble advocate until the end of his life, he voiced his objections when former NASA administrator Sean O'Keefe ruled out additional shuttle missions to repair the orbiting observatory. In February, he and two colleagues published an article in the Los Angeles Times urging Congress to restore the funds to keep the Hubble in operation.
"If money is not restored to fix Hubble, then one of the world's most productive scientific instruments will forever close its eye on the universe," they wrote. "What is at stake is not only a piece of stellar technology but our commitment to the most fundamental human quest: understanding the cosmos."
Current NASA administrator Michael Griffin has agreed to reconsider the issue.
John Norris Bahcall was born in Shreveport, La., on Dec. 30, 1934. He enrolled at Louisiana State University, where he considered studying philosophy and becoming a rabbi. He left LSU after a year and enrolled at Berkeley.
In his Berkeley commencement address, he recalled arriving at the university never having taken a science course. In high school, he said, "my job was to play tennis." The university required that he take at least one science course, so he enrolled in physics.
"It was the hardest thing I have ever done in my life," he said, "but I fell in love with science. I was thrilled by the fact that by knowing physics you could figure out how real things worked, like sunsets and airplanes, and that after a while everyone agreed on what was the right answer to a question."
He received a bachelor's degree from Berkeley in 1956, a master's degree in physics from the University of Chicago in 1957 and a PhD in physics from Harvard University in 1961. He was a research fellow at Indiana University before joining the faculty at Cal Tech.
In 1968, he joined the Institute for Advanced Study, where he worked on several areas of astrophysics, including the study of dark matter in the universe and the evolution of stars. Becoming a faculty member in 1971, he trained a number of astrophysicists who have become leaders in the field. He also helped establish astronomy groups at the Weizmann Institute of Science, Tel Aviv University and elsewhere.
Dr. Bahcall was the recipient of numerous science awards, including the National Medal of Science, awarded by President Bill Clinton in 1998. Many of his colleagues expected him to win a Nobel Prize. Although Davis, his friend and collaborator, shared the 2002 prize with Masatoshi Koshiba, a Japanese neutrino researcher, Dr. Bahcall was not included. Friends reported that he was not bitter.
Survivors include his wife of 38 years, Dr. Neta Bahcall, a professor of astrophysics at Princeton; two sons, Dr. Safi Bahcall of New York City and Dr. Dan Bahcall of Berkeley; a daughter, Dr. Orli Bahcall of New York City; and a brother.