Magnetic fields in superdense stars: cyclotron resonance emission

Huge magnetic fields greatly exceeding those achieved in the laboratory exist at the surface of many collapsed stars. There are 16 known ''magnetic'' white dwarfs with magnetic fields in the range 107-108G or above. Neutron stars observed as isolated pulsars or by their accretion from a very close binary companion have surface fields of order 1012G (although their total flux seems comparable to that of the dwarfs). The huge fields of the white dwarfs are indicated by very large observed Zeeman splitting or continuum circular polarization. The neutron star fields have generally been inferred from the torques needed to account for the measured stellar spin-down rates. The electron cyclotron resonance in a 5 X 1012G field is at 53 keV. A measured X-ray emission line at that energy has been associated with the magnetosphere or surface of the spinning accreting neutron star in Hz Her and is presumed to originate in the cyclotron emission of free electrons of the column of accreting matter near the stellar surface. Fields greater than 1012G lead to expected properties and phenomena which have not been seen in the laboratory but which appear to have observable consequences for neutron star observations. The large density (approximately 104-105g/cm3) and lattice-binding energy (2-5 keV) of matter in such a huge magnetic field causes the stellar surface to be sharp and mirror-like for X-rays and also to be able to retain ions despite electric fields of 108V/cm as long as its temperature does not exceed several million degrees These features should have observable consequences for X-ray binaries and pulsars. (Auth.)