Born in New York City, Oppenheimer obtained a degree in chemistry from Harvard University in 1925 and a doctorate in physics from the University of Göttingen in Germany in 1927, studying under Max Born. After research at other institutions, he joined the physics faculty at the University of California, Berkeley, where he was made a full professor in 1936. Oppenheimer made significant contributions to physics in the fields of quantum mechanics and nuclear physics, including the Born–Oppenheimer approximation for molecular wave functions ; work on the theory of positrons, quantum electrodynamics, and quantum field theory ; and the Oppenheimer–Phillips process in nuclear fusion. With his students, he also made major contributions to astrophysics, including the theory of cosmic ray showers, and the theory of neutron stars and black holes.