Solar and Supernova Neutrinos

Abstract

Ever since it was realized in the 1920’s that nuclear fusion reactions are the only viable source that could power the Sun for a time compatible with the age of the oldest rocks found on Earth, the production and emission of neutrinos is closely related to the stellar evolution. During the time when a star is on the main sequence, i.e. follows the most common evolution pattern, neutrinos are constantly emitted by the same fusion reactions, that provide the energy for its luminosity. For all ordinary stars, similar to the Sun, the emitted neutrino fluxes are almost directly proportional to the stellar luminosity. A very simple estimate gives the magnitude of the neutrino flux from the Sun. If we assume that the first fusion reaction that puts together protons to create a deuteron,

$$ p + p \to {}^2H + {e^ + } + {v_e} + 1.44MeV $$

((1))

is the only energy source of the Sun, we can calculate the flux of v _e at Earth. The total amount of energy created by this reaction is ~ 10 MeV. The reaction rate is then

$$ Rate = {L_ \odot }/10MeV = 2.5 \times 1{0^{38}}{s^{ - 1}}, $$

((2))

and the neutrino flux F _v

$$ {F_v} \simeq {{2.5 \times {{10}^{38}}} \over {4\pi {D^2}}} \simeq {10^{11}}c{m^{ - 2}}{s^{ - 1}}. $$

((3))

This number is surprisingly close to the real flux of solar neutrinos.