Nucleosynthesis basics and applications to supernovae

Abstract

This review concentrates on nucleosynthesis processes in general and their applications to massive stars and supernovae. A brief initial introduction is given to the physics in astrophysical plasmas which governs composition changes. We present the basic equations for thermonuclear reaction rates and nuclear reaction networks. The required nuclear physics input for reaction rates is discussed, i.e. cross sections for nuclear reactions, photodisintegrations, electron and positron captures, neutrino captures, inelastic neutrino scattering, and beta-decay half-lives. We examine especially the present state of uncertainties in predicting thermonuclear reaction rates, while the status of experiments is discussed by others in this volume (see M. Wiescher). It follows a brief review of hydrostatic burning stages in stellar evolution before discussing the fate of massive stars, i.e. the nucleosynthesis in type II supernova explosions (SNe II). Except for SNe Ia, which are explained by exploding white dwarfs in binary stellar systems (which will not be discussed here), all other supernova types seem to be linked to the gravitational collapse of massive stars (M>8M ) at the end of their hydrostatic evolution. SN1987A, the first type II supernova for which the progenitor star was known, is used as an example for nucleosynthesis calculations. Finally, we discuss the production of heavy elements in the r-process up to Th and U and its possible connection to supernovae.

EXPLOSIVE NUCLEOSYNTHESIS IN THE NEUTRINO-DRIVEN ASPHERICAL SUPERNOVA EXPLOSION OF A NON-ROTATING 15M☉STAR WITH SOLAR METALLICITY

“…Figure 3(a) shows ρ max as a function of T max of the ejecta for L νe = 4.5 × 10 52 erg s −1 . Most of the ejecta with relatively low densities (< 10 8 g cm −3 ) have ρ max and T max similar to those of ejecta in the spherical model of core collapse SNe (Thielemann et al 1998). For some particles that have very high densities simultaneously with high temperatures (ρ max ≥ 10 9 g cm −3 and T max ≥ 10 10 K), electron captures operate to some extent, so that these particles become slightly neutron-rich, Y e (10, 000 km) < 0.48.…”

Supernovae from Massive Stars

“…Because of the high temperatures, these light particles can be captured by almost all the isotopes present in the hot plasma and therefore huge number of nuclear reactions are promptly activated. The general properties of the advanced burning stages in massive stars are discussed in details in many papers and excellent reviews [2,9,5,10,13].…”

Spin–isospin excitations and half-lives of medium-mass deformed nuclei

“…In this context, the betadecay properties of these exotic objects are of extreme importance in two different aspects. First, most nuclei of astrophysical interest [2] are those far from stability and their beta-decay rates have to be estimated theoretically. Second, beta-decay properties and nuclear structure are intimately related.…”