Cooling of Neutron Stars with Color Superconducting Quark Cores

Abstract

We show that within a recently developed nonlocal chiral quark model the critical density for a phase transition to color superconducting quark matter under neutron star conditions can be low enough for these phases to occur in compact star configurations with masses below 1.3 M_sun. We study the cooling of these objects in isolation for different values of the gravitational mass and argue that, if the quark matter phase would allow unpaired quarks, the corresponding hybrid stars would cool too fast. The comparison with observational data puts tight constraints on possible color superconducting quark matter phases. Possible candidates with diquark gaps of the order of 10 keV - 1 MeV such as the "2SC+X" and the color spin locking (CSL) phase are presented.Comment: 4 pages, 1 figure, prepared for the Proceedings of Quark Matter 2005, August 4 - 9, Budapest, Hungar

Hybrid stars in an SU(3) parity doublet model

“…As discussed above we consider only small gap values (∆ = 10 MeV), which have little effect to the EoS. In that sense our pairing model is similar (but not exactly equal) to that discussed in [83], labeled 2SC+x, where we have a 2SC pairing of the u and d of two colors, and a residual pairing of the remaining unpaired quark, leading to the effective pairing of all u and d quarks.…”

Nonlocality effects on color spin locking condensates

“…The DU conflict would be solved provided no ungapped quark modes occur in the quark core. This has been demonstrated on the example of a hypothetical pairing channel (X-gap) for the quark color which is ungapped in the 2SC phase (2 SC X phase) [10,11]. However, the microscopic origin of the X-gap could not yet be specified.…”

Strange quark matter and compact stars

“…As pointed out by Prakash et al [274], this upper limit can be fit with standard neutrino cooling (like n + n → n + p + e − +ν e ) plus pair-breaking and formation, but the luminosity and ages of other neutron stars cannot be simultaneously fit using the same equation of state [298,299] which has the interesting consequence that more exotic, rapid cooling processes may exist in the core of PSR 0205+6449. Physical processes which would enable such a rapid drop in temperature range from the presence of meson condensates [188,300], to quark matter [40,301,302], to the direct Urca process [303]. (For a very recent overview on neutron star cooling, see Ref.…”

“…These quarks may thus not pair but, instead, may radiate neutrinos rapidly via the quark direct Urca process shown in table 6. If this is the case, the 2SC quark matter core will cool rapidly and determine the cooling history of the star [26,302]. Examples of cooling curves of neutron stars containing quark matter in the 2SC phase are shown in Figs.…”