arXiv subjects

M. E. Gusakov

Publications and source records attributed to M. E. Gusakov.

40 records · Page 3Linked to original sources

arXiv2004

Direct Urca Process in a Neutron Star Mantle

We show that the direct Urca process of neutrino emission is allowed in two possible phases of nonspherical nuclei (inverse cylinders and inverse spheres) in the mantle of a neutron star near the crust-core interface. The process is open because neutrons and protons move in a periodic potential created by inhomogeneous nuclear structures. In this way the nucleons acquire large quasimomenta needed to satisfy momentum-conservation in the neutrino reaction. The appropriate neutrino emissivity in a nonsuperfluid matter is about 2--3 orders of magnitude higher than the emissivity of the modified Urca process in the stellar core. The process may noticeably accelerate the cooling of low-mass neutron stars.

astro-ph↗

arXiv2004

Enhanced cooling of neutron stars via Cooper-pairing neutrino emission

We simulate cooling of superfluid neutron stars with nucleon cores where direct Urca process is forbidden. We adopt density dependent critical temperatures $T_{cp}(ρ)$ and $T_{cn}(ρ)$ of singlet-state proton and triplet-state neutron pairing in a stellar core and consider a strong proton pairing (with maximum $T_{cp}^{max} \ga 5 \times 10^9$ K) and a moderate neutron pairing ($T_{cn}^{max} \sim 6 \times 10^8$ K). When the internal stellar temperature $T$ falls below $T_{cn}^{max}$, the neutrino luminosity $L_{CP}$ due to Cooper pairing of neutrons behaves $\propto T^8$, just as that produced by modified Urca process (in a non-superfluid star) but is higher by about two orders of magnitude. In this case the Cooper-pairing neutrino emission acts like an enhanced cooling agent. By tuning the density dependence $T_{cn}(ρ)$ we can explain observations of cooling isolated neutron stars in the scenario in which direct Urca process or similar process in kaon/pion condensed or quark matter are absent.

astro-ph↗

arXiv2002

Cooling of Neutron Stars: Two Types of Triplet Neutron Pairing

We consider cooling of neutron stars (NSs) with superfluid cores composed of neutrons, protons, and electrons (assuming singlet-state pairing of protons, and triplet-state pairing of neutrons). We mainly focus on (nonstandard) triplet-state pairing of neutrons with the $|m_J| = 2$ projection of the total angular momentum of Cooper pairs onto quantization axis. The specific feature of this pairing is that it leads to a power-law (nonexponential) reduction of the emissivity of the main neutrino processes by neutron superfluidity. For a wide range of neutron critical temperatures $T_{cn}$, the cooling of NSs with the $|m_J| = 2$ superfluidity is either the same as the cooling with the $m_J = 0$ superfluidity, considered in the majority of papers, or much faster. The cooling of NSs with density dependent critical temperatures $T_{cn}(ρ)$ and $T_{cp}(ρ)$ can be imitated by the cooling of the NSs with some effective critical temperatures $T_{cn}$ and $T_{cp}$ constant over NS cores. The hypothesis of strong neutron superfluidity with $|m_J| = 2$ is inconsistent with current observations of thermal emission from NSs, but the hypothesis of weak neutron superfluidity of any type does not contradict to observations.

astro-ph↗

arXiv2002

Neutrino Emission from Superfluid Neutron-Star Cores: Various Types of Neutron Pairing

We calculate and provide analytic fits of the factors which describe the reduction of the neutrino emissivity of modified Urca and nucleon-nucleon bremsstrahlung processes by superfluidity of neutrons and protons in neutron-star cores. We consider $^1$S$_0$ pairing of protons and either $^1$S$_0$ or $^3$P$_2$ pairing of neutrons. We analyze two types of $^3$P$_2$ pairing: the familiar pairing with zero projection of the total angular momentum of neutron pairs onto quantization axis, $m_J=0$; and the pairing with $|m_J|=2$ which leads to the gap with nodes at the neutron Fermi surface. Combining the new data with those available in the literature we fully describe neutrino emission by nucleons from neutron star cores to be used in simulations of cooling of superfluid neutron stars.

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