Engineering topics

Cooperstein, J.

Publications and source records attributed to Cooperstein, J..

5 records

NASA NTRS1992

Flux-limited diffusion in hydrodynamics

The radiation transport equation, correct to order v/c, is used to derive a flux limiter valid in high-velocity hydrodynamic flows. In the limit v = 0 the widely used result of Levermore and Pomraning (LP) (1982) is recovered. In the case of homologous flow (v varies as R) the LP result remains valid, but in the presence of shock waves and other nonhomologous flows differences may be large. We calculate the Eddington factors, which are significantly altered, and discuss the importance of having them possess the correct form in the presence of a shock wave, e.g., on the neutrino transport during the formation of a supernova.

Cooperstein, J.↗

NASA NTRS1987

Neutrino pair energy deposition in supernovae

The role of neutrino-antineutrino annihilation (producing an electron-positron pair) in delayed type II supernova explosions is investigated theoretically. The assumptions and analysis of Goodman et al. (1987) are examined in detail, with a focus on the need for a large density gradient at the edge of the neutrinosphere. It is found that the neutrino annihilation mechanism cannot contribute significantly to the energy of the explosion.

Cooperstein, J.↗

NASA NTRS1987

Collapse of 9 solar mass stars

General relativistic hydrodynamical calculations of the collapse of O + Ne + Mg cores of a 9 solar mass star are reported. Collapse is induced by rapid electron captures as the O + Ne + Mg is burned to nuclear statistical equilibrium. The high entropy in the core after burning leads to a large abundance of free protons which readily capture electrons. This leads to large neutrino losses and a correspondingly small infalling homologous core. The hydrodynamic shock thus forms at a small mass point. The shock stalls before reaching the edge of the O + Ne + Mg core and thereby fails to produce a successful supernova explosion by the direct mechanism. No enhancement in the shock energy due to nuclear burning is found.

Baron, E.↗

NASA NTRS1987

Collapsing white dwarfs

The results of the hydrodynamic collapse of an accreting C + O white dwarf are presented. Collapse is induced by electron captures in the iron core behind a conductive deflagration front. The shock wave produced by the hydrodynamic bounce of the iron core stalls at about 115 km, and thus a neutron star formed in such a model would be formed as an optically quiet event.

Baron, E.↗

NASA NTRS1987

Type-II supernovae from prompt explosions

Evidence is cited that supernova 1987A involved a large explosion energy, of about (2-3) x 10 to the 51st ergs. Such large explosion energy has not come from delayed shocks to date, nor is it likely to. Improved physics in the presupernova evolution, especially the inclusion of Coulomb interactions, has brought the iron-core mass down by less than about 0.1 solar mass in the 13 solar mass star which has recently been evolved. It is found that supernova explosion energies up to 3 x 10 to the 51st ergs can be obtained by the prompt-explosion mechanism, provided that a somewhat soft equation of state is used at supranuclear densities.

Baron, E.↗