Influence of the stiffness of the equation of state and in-medium effects on the cooling of compact stars

Abstract

Abstract. Measurements of the low masses for the pulsar PSR J0737-3039B, for the companion of PSR J1756-2251 and for the companion of PSR J0453+1559 on the one hand and of the high masses for the pulsars PSR J1614-2230 and PSR J0348-0432 on the other demonstrate the existence of compact stars with masses in a broad range from 1.2 to 2 M . The most massive of these objects might be hybrid stars. To fulfill the constraint Mmax > 2 M with a reserve we exploit the stiff DD2 hadronic equation of state (EoS) without and with excluded volume (DD2vex) correction, which produce maximum neutron star masses of Mmax = 2.43 M and 2.70 M , respectively. We show that the stiffness of the EoS does not preclude an explanation of the whole set of cooling data within "nuclear medium cooling" scenario for compact stars by a variation of the star masses. We select appropriate proton gap profiles from those exploited in the literature and allow for a variation of the effective pion gap controlling the efficiency of the medium modified Urca process. However, we suppress the possibility of pion condensation. In general, the stiffer the EoS the steeper a decrease with density of the effective pion gap is required. Results are compared with previously obtained ones for the HDD EoS for which Mmax = 2.06 M . The cooling of the compact star in the supernova remnant Cassiopeia A (Cas A) is explained mainly by an efficient medium modified Urca process. To explain a > ∼ 2.5% decline of the cooling curve for Cas A, as motivated by an analysis of the ACIS-S instrument data, together with other cooling data exploiting the DD2 EoS a large proton gap at densities n < ∼ 2n0 is required vanishing for n > ∼ 2.5 n0, where n0 is the saturation nuclear density. A smaller decline, as it follows from an analysis of the HRC-S instrument data, is explained with many choices of parameters. With the DD2vex EoS and using an effective pion gap steeper decreasing with the density and/or a proton gap shifted to smaller densities we are also able to reproduce both a strong decline compatible with ACIS-S data and HRC-S instrument data. The mass of Cas A is estimated as 1.6 − 1.9 M , above the value 1.5 M , which we have evaluated with the softer HDD equation of state. Different mass choices for the hottest object XMMU J173203.3-344518 are discussed. We make general remarks also on hybrid star cooling and on its dependence on the stiffness of the hadronic EoS.PACS. 97.60.Jd Neutron stars -95.30.Cq Elementary particle processes -26.60-c Nuclear matter aspects of neutron stars

On Manifestation of In-Medium Effects in Neutron Stars and Heavy-Ion Collisions

“…The pairing 1S 0 gaps correspond to calculations with the EEHO model, cf. similar results of calculations with DD2 EoS in Figure 3 of [86]. [87].…”

“…The results of calculations were confronted to the data [67,[82][83][84][85][86] demonstrating an overall agreement of calculations with the data already without necessity to include the DU channel. An example of such calculations is presented in Figure 11, where the cooling curves are shown being computed with MKVOR EoS [87].…”

On Cooling of Neutron Stars with a Stiff Equation of State Including Hyperons

“…Besides, we should bear in mind that the pairing suppression R-factors for the DU processes on nucleons and hyperons are different and in our model, for the EoS in the region in which there are hyperons, the R-factor for DU processes on nucleons is larger than that on hyperons. We adopt here all cooling inputs such as the neutrino emissivities, specific heat, crust properties, etc., from our earlier works performed on the basis of the HHJ equation of state (EoS) [11,14,15], a stiffer HDD EoS [16] and even stiffer DD2 and DD2vex EoSs [17] for the hadronic matter. These works exploit the nuclear medium cooling scenario, where the most efficient processes are the medium-modified Urca (MMU) processes, nn → npeν and np → ppeν, medium-modified nucleon bremstrahlung (MNB) processes nn → nnνν, np → npνν, pp → ppνν, and the pair-breaking-formation (PBF) processes n → nνν and p → pνν.…”

“…Within our scenario, we continue to exploit the assumption that the value of the 3 P 2 nn pairing gap is tiny and its actual value does not affect the calculations of the neutrino emissivity [14]. For calculation of the proton pairing gaps, we use the same models as in [17] but now we exploit EoSs of the MKVORHφ model. The corresponding gaps are shown on the left panel in Figure 2.…”

Neutrino emissivities and bulk viscosity in neutral two-flavor quark matter

“…Refs. [34,35]. If quark matter is present in the CS interior we expect it to be in a color-superconducting state which entails a strong dependence on the pairing pattern and the sizes of pairing gaps.…”