Central temperature of the Sun can be measured via theBe7solar neutrino line

A precise test of the theory of stellar evolution can be performed by measuring the difference in average energy between the neutrino line produced by ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ electron capture in the solar interior and the corresponding neutron line produced in a terrestrial laboratory. The high temperatures in the center of the Sun broaden the line asymmetrically, FWHM =1.6 keV, and cause an average energy shift of 1.3 keV. The width of the ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ neutrino line should be taken into account in calculations of vacuum neutrino oscillations.