13,356 research outputs found
Theory of Disk Accretion onto Magnetic Stars
Disk accretion onto magnetic stars occurs in a variety of systems, including
accreting neutron stars (with both high and low magnetic fields), white dwarfs,
and protostars. We review some of the key physical processes in
magnetosphere-disk interaction, highlighting the theoretical uncertainties. We
also discuss some applications to the observations of accreting neutron stars
and protostellar systems, as well as possible connections to protoplanetary
disks and exoplanets.Comment: 13 pages, 5 figures. EPJ Web of Conferences (Vol.64) "Physics at the
Magnetospheric Boundary", Geneva, Switzerland, 25-28 June, 2013, eds. E.
Bozzo et al.
http://www.epj-conferences.org/index.php?option=com_toc&url=/articles/epjconf/abs/2014/01/contents/contents.htm
Resonant Oscillations and Tidal Heating in Coalescing Binary Neutron Stars
Tidal interaction in a coalescing neutron star binary can resonantly excite
the g-mode oscillations of the neutron star when the frequency of the tidal
driving force equals the intrinsic g-mode frequencies. We study the g-mode
oscillations of cold neutron stars using recent microscopic nuclear equations
of state, where we determine self-consistently the sound speed and
Brunt-V\"ais\"al\"a frequency in the nuclear liquid core. The properties of the
g-modes associated with the stable stratification of the core depend
sensitively on the pressure-density relation as well as the symmetry energy of
the dense nuclear matter. The frequencies of the first ten g-modes lie
approximately in the range of Hz. Resonant excitations of these
g-modes during the last few minutes of the binary coalescence result in energy
transfer and angular momentum transfer from the binary orbit to the neutron
star. The angular momentum transfer is possible because a dynamical tidal lag
develops even in the absence of fluid viscosity. However, since the coupling
between the g-mode and the tidal potential is rather weak, the amount of energy
transfer during a resonance and the induced orbital phase error are very small.
Resonant excitations of the g-modes play an important role in tidal heating of
binary neutron stars. Without the resonances, viscous dissipation is effective
only when the stars are close to contact. The resonant oscillations result in
dissipation at much larger orbital separation. The actual amount of tidal
heating depends on the viscosity of the neutron star. Using the microscopic
viscosity, we find that the binary neutron stars are heated to a temperature
K before they come into contact.Comment: 35 pages, TeX (MNRAS in press). Cornell CRSR-106
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