Radiative processes in an intense magnetic field

Abstract

Three astrophysical problems relating to the intense magnetic fields associated with neutron stars (i.e. 1012 gauss) and white dwarfs (i.e. 108 gauss) are studied. (1) The radiation rate for non-relativistic bremsstrahlung in 1012 gauss is computed by both quantum-mechanical and classical methods. The main features of this emissivity are a 1/pz dependence (magnetic field in the z-direction) characteristic of a one-dimensional momentum space, a larger flux perpendicular to Җ than parallel to it, and a net left-handed polarization in the flux parallel to Җ. (2) The electron energy levels and orbits for hydrogen in 1012 gauss are calculated with variational techniques. The ground state binding energy is found to be 200 ev. The other levels divide into a set of tightly bound states (binding energies 100 to 200 ev) and a double-set of hydrogen-like levels (0 to 13 ev). The overall electron density of the atom is elongated along the magnetic field direction. The thermal ionization fraction of a neutral hydrogen plasma is computed using an appropriately modified Saha equation, and is found to be 90%. Finally, high Z atoms are investigated via the Thomas-Fermi approximation with the result that the definitive equation is X11 = X1/2x1/2 giving an atomic radius of R = 4 x 10-5 Z1/5 Җ2/5 cm. (3) Cyclotron emission and absorption in a magnetic field of 108 gauss is studied as a possible mechanism for the observed degree of circular polarization in the optical emission from white dwarfs. A few simple models explain some of the quantitative and qualitative aspects of the polarization data.