Effects of the quark-hadron phase transition on highly magnetized neutron stars

Abstract

The presence of quark-hadron phase transitions in neutron stars can be related to several interesting phenomena. In particular, previous calculations have shown that fast rotating neutron stars, when subjected to a quark-hadron phase transition in their interiors, could give rise to the backbending phenomenon characterized by a spin-up era. In this work, we use an equation of state composed of two phases, containing nucleons (and leptons) and quarks. The hadronic phase is described in a relativistic mean field formalism that takes many-body forces into account, and the quark phase is described by the MIT bag model with a vector interaction. Stationary and axisymmetric stellar models are obtained in a self-consistent way by solving numerically the Einstein-Maxwell equations by means of a pseudo-spectral method. As a result, we obtain the interesting backbending phenomenon for fast spinning neutron stars. More importantly, we show that a magnetic field, which is assumed to be axi-symmetric and poloidal, can also be enhanced due to the phase transition from normal hadronic matter to quark matter on highly magnetized neutron stars. Therefore, in parallel to the spin-up era, classes of neutron stars endowed with strong magnetic fields may go through a "magnetic-up era" in their lives.

The population of highly magnetized neutron stars

“…In such stars, the central region does not provide enough energy to reach the hyperons threshold of appearance. Similar results have already been discussed in the literature for highly magnetized hybrid stars, proving that strong magnetic fields can also prevent the occurance of phase transitions in such objects [22,24]. Furthermore, although not investigated in this work, the microscopic effects of Landau quantization in the EoS also shifts the threshold of the appearance of hyperons to higher densities due to the extra magnetic contribuition to the particles energy levels [2,7,28].…”

“…Such effect can have a severe impact on the population of highly magnetized neutron stars. The decrease of the central chemical potential, related to the baryon density, can prevent the appearance of phase transitions [22,24] as well as the existence of exotic degrees of freedom. In this work, we show for a particular parametrization of the many-body forces model (MBF model) that the hyperon population of neutron stars is completely supressed in the presence of central magnetic fields B c ∼ 10 18 G.…”

Constraining Strangeness in Dense Matter with GW170817

“…The MBF model reproduces both nuclear matter properties at saturation and the observational properties of neutron stars with hyperons [2] and magnetic hybrid stars [55,131]. For this work, the following nuclear properties at saturation were used: binding energy per nucleon B/A = −15.75 MeV, saturation density ρ 0 = 0.15 fm −3 , symmetry energy and its slope a 0 sym = 32 MeV and L 0 = 97 MeV, respectively.…”

Effects of magnetic fields in white dwarfs

“…The Lorentz force is the derivative of the magnetic potential M(r, θ) in the equation Eq. (14) and reaches its maximum value off-center (r eq ∼ 350 km, see Fig. 2).…”