13 research outputs found
Accretion by Isolated Neutron Stars
Accretion of interstellar material by an isolated neutron star is discussed.
The point I address here is the interaction between the accretion flow and the
stellar magnetosphere. I show that the interchange instabilities of the
magnetospheric boundary under the conditions of interest are basically
suppressed. The entry of the material into the magnetosphere is governed by
diffusion. Due to this reason the persistent accretion luminosity of isolated
neutron stars is limited to < 4E+26 erg/s. These objects can also appear as
X-ray bursters with the burst durations of about 30 minutes and repetition time
of about 1E+5 yr. This indicates that the number of the accreting isolated
neutron stars which could be observed with recent and modern X-ray missions is
a few orders of magnitude smaller than that previously estimated.Comment: 3 pages, to appear in Astrophysics and Space Science, in the
proceedings of "Isolated Neutron Stars: from the Interior to the Surface",
edited by D. Page, R. Turolla and S. Zan
Current Status of Simulations
As the title suggests, the purpose of this chapter is to review the current
status of numerical simulations of black hole accretion disks. This chapter
focuses exclusively on global simulations of the accretion process within a few
tens of gravitational radii of the black hole. Most of the simulations
discussed are performed using general relativistic magnetohydrodynamic (MHD)
schemes, although some mention is made of Newtonian radiation MHD simulations
and smoothed particle hydrodynamics. The goal is to convey some of the exciting
work that has been going on in the past few years and provide some speculation
on future directions.Comment: 15 pages, 14 figures, to appear in the proceedings of the ISSI-Bern
workshop on "The Physics of Accretion onto Black Holes" (8-12 October 2012