Viscous damping ofr-mode oscillations in compact stars with quark matter

Abstract

We determine characteristic timescales for the viscous damping of r-mode oscillations in rapidly rotating compact stars that contain quark matter. We present results for the color-flavor-locked (CFL) phase of dense quark matter, in which the up, down and strange quarks are gapped, as well as the normal (ungapped) quark phase. While the ungapped quark phase supports a temperature window 10 8 K ≤ T ≤ 5 × 10 9 K where the r-mode is damped even for rapid rotation, the r-mode in a rapidly rotating pure CFL star is not damped in the temperature range 10 10 K≤ T ≤ 10 11 K. Rotating hybrid stars with quark matter cores display an instability window whose width is determined by the amount of quark matter present, and they can have large spin frequencies outside this window. Except at high temperatures T ≥ 10 10 K, the presence of a quark phase allows for larger critical frequencies and smaller spin-periods compared to rotating neutron stars. If low-mass X-ray binaries contain a large amount of ungapped or CFL quark matter, then our estimates of the r-mode instability suggest that there should be a population of rapidly rotating binaries at ν 1000 Hz which have not yet been observed.

Thickness of the strangelet-crystal crust of a strange star

“…[33] found that the strangelet crystal crust did not have the right spectrum of toroidal shear modes to account for current observations: it would be interesting to see whether taking in to account the surface tension and Debye screening affects that conclusion. Other aspects of the phenomenology of the crust could also be studied, for example (a) the thermal response of the crust to accretion [35]; (b) the role of the crust in the trapping of neutrinos and photons just after a type-II supernova [36]; (c) the spectrum of photons radiated from the surface of a quark star [37,38,39]; (d) the contribution of the crust to the moment of inertia and glitches [40]; (e) the damping of r-modes in by shear viscosity in the crust [41,42] (for quark stars, the contribution from the interior has been calculated [43,44]); (f) the thermal relaxation time of the crust and its response to the postsupernova "cooling wave" [45]. The thermal relaxation time of the crust depends on the thermal conductivity, for which we can make a very rough estimate using appendix A of Ref.…”

Quark matter in neutron stars

“…3, which is taken from Ref. [41]. We see that the forbidden region for various models of nuclear matter (left panel) is quite different from that for models of hybrid stars (right panel).…”

Bulk viscosity coefficients due to phonons and kaons in superfluid color-flavor locked quark matter

“…Using Eqs. (7), (8), (28), and (29), we find that the real part of the viscosities can be expressed as…”

“…(7), (8), (28), and (29), one can find the real part of the viscosities. In this case we find that the frequency dependence of the coefficients is different from the case where only the kaons (or phonons) are considered.…”