Photo of John N. Bahcall

John N. Bahcall

  • National Medal of Science
  • Physical Sciences
For his fundamental contributions to areas of modern astrophysics ranging from solar neutrino physics to the structure of the Milky Way Galaxy to cosmology, and for his leadership of the astronomical community, especially his tireless advocacy of the Hubble Space Telescope.

The sun is a large fusion reactor, producing the energy responsible for life on Earth. Scientists predicted sunlight is produced by four hydrogen protons transforming into a helium nucleus, and particles called neutrinos, a neutral particle smaller than an atom. As helium’s nucleus contains two protons, it was deduced that two of the four hydrogen protons become neutrons by releasing a neutrino and antineutrino.rnrnIn 1964, John N. Bahcall collaborated with astrophysicist Raymond Davis Jr to provide evidence for this theory of sunlight production. They designed a computer model capable of reflecting the sun’s actual neutrino count and then compared the value to one they obtained by monitoring the neutrino count of decaying argon in a closed system. In 1968, Davis reported there was only about a third of neutrinos present than predicted. This discrepancy signaled that either Bahcall and Davis’s calculation was wrong, or neutrinos acted differently than previously assumed.rnrnIn 2001, researchers solved the neutrino problem, explaining that these neutrinos never went missing—they actually transformed into muon and tau neutrinos, particles that are more difficult to detect than the electron neutrinos Bahcall and Davis expected to see. Through this experiment, physicists revised their understanding about neutrinos.rnrnBy Kristen Brida