Neutrino trapping in extremely compact Tolman VII spacetimes

Extremely compact objects trap gravitational waves or neutrinos, assumed to move along null geodesics in the trapping regions. The trapping of neutrinos was extensively studied for spherically symmetric extremely compact objects constructed under the simplest approximation of the uniform energy density distribution, with radius located under the photosphere of the external spacetime; in addition, uniform emissivity distribution of neutrinos was assumed in these studies. Here we extend the studies of the neutrino trapping for the case of the extremely compact Tolman VII objects representing the simplest generalization of the internal Schwarzschild solution with uniform distribution of the energy density, and the correspondingly related distribution of the neutrino emissivity that is thus again proportional to the energy density; radius of such extremely compact objects can overcome the photosphere of the external Schwarzschild spacetime. In dependence on the parameters of the Tolman VII spacetimes, we determine the “local” and “global” coefficients of efficiency of the trapping and demonstrate that the role of the trapping is significantly stronger than in the internal Schwarzschild spacetimes. Our results indicate possible influence of the neutrino trapping in cooling of neutron stars.

Transport Properties of Superfluid Phonons in Neutron Stars

We review the effective field theory associated with the superfluid phonons that we use for the study of transport properties in the core of superfluid neutrons stars in their low temperature regime. We then discuss the shear and bulk viscosities together with the thermal conductivity coming from the collisions of superfluid phonons in neutron stars. With regard to shear, bulk, and thermal transport coefficients, the phonon collisional processes are obtained in terms of the equation of state and the superfluid gap. We compare the shear coefficient due to the interaction among superfluid phonons with other dominant processes in neutron stars, such as electron collisions. We also analyze the possible consequences for the r-mode instability in neutron stars. As for the bulk viscosities, we determine that phonon collisions contribute decisively to the bulk viscosities inside neutron stars. For the thermal conductivity resulting from phonon collisions, we find that it is temperature independent well below the transition temperature. We also obtain that the thermal conductivity due to superfluid phonons dominates over the one resulting from electron-muon interactions once phonons are in the hydrodynamic regime. As the phonons couple to the Z electroweak gauge boson, we estimate the associated neutrino emissivity. We also briefly comment on how the superfluid phonon interactions are modified in the presence of a gravitational field or in a moving background.

Warm dense matter and cooling of supernovae remnants

We study the thermal effects on the nuclear matter (NM) properties such as binding energy, incompressibility, free symmetry energy and its coefficients using NL3, G3 and IU-FSU parameter sets of relativistic mean-field models. These models being consistent with the properties of cold NM, have also been used to study the effect of temperature by incorporating the Fermi function. The critical temperature for the liquid-gas phase transition in the symmetric NM is found to be 14.60, 15.37 and 14.50 MeV for NL3, G3 and IU-FSU parameter sets respectively, which is in excellent agreement with previous theoretical and experimental studies. We inspect that the properties related to second differential coefficient of the binding energy and free symmetry energy at saturation density ( i.e. $$K_{0}(n,T)$$K0(n,T) and $$Q_{sym,0}$$Qsym,0 ) exhibit the contrary effects for NL3 and G3 parameters as the temperature increases. We find that the prediction of saturated curvature parameter ( $$K_{sym,0}$$Ksym,0 ) for G3 equation of state at finite temperature favour the combined analysis of $$K_{sym,0}$$Ksym,0 for the existence of massive pulsars, gravitational waves from GW170817 and NICER observations of PSR J0030+0451. Further, we investigate the cooling mechanism of newly born stars through neutrino emissivity controlled by direct Urca process and instate some interesting remarks about neutrino emissivity. We also deliberate the effect of temperature on the M-R profile of Proto-Neutron star.

The role of magnetic fields in the formation and propagation of hadronic microquasars jets

In the present work, we examine the role of the magnetic field (MF), which causes a rather pronounced confinement of the jets at microquasars. Due to radial Lorentz forces acting on the jet’s matter towards the jet’s axis, the outgoing flux is collimated along the same axis and vertically to the compact object. Alternatively, a rotating central object may drag the surrounding MF into collimation around the produced jet. In such objects, jet emerges from each side of the accretion disc.These jets operate as cosmic engines, capable of accelerating particles on very high energies (~10^2 TeV) and consist sources of high energy neutrinos and gamma rays. We also examine the role of the MF, which causes to a rather pronounced jet confinement. Our aim is to investigate and model its role on various physical observables of the jet, by simulating the jet’s flow and derive 2D and 3D visualizations and furthermore examine its effect on the neutrino emissivity.