The evolution of radiation-dominated stars. I - Nonrotating supermassive stars

The evolution of nonrotating supermassive stars (M approximately equal to or greater than 5 x 10 to the 4th solar masses) is examined in detail using the results of hydrodynamic calculations which include post-Newtonian approximations to general relativistic gravity, an equation of state which includes electron-positron pairs, and all relevant nuclear reactions. These calculations are followed through the period of quasi-static contraction, the general relativistic instability, and the eventual collapse to a black hole or disruption via a thermonuclear explosion. It is found that stars with mass M equal to or greater than 10 to the 5th solar masses and initial metallicities Z equal to or less than 0.005 do not explode. The objects with Z equal to or greater than 0.005 do explode because of the burning hydrogen by the beta-limited CNO cycle. Explosion energies range from 2.0 x 10 to the 56th ergs for stars of mass M about 10 to the 5th solar masses to 2.5 x 10 to the 57th ergs for M about 10 to the 6th solar masses. For those stars that do not explode the collapse to a black hole is found to be nonhomologous.