Effects of strong magnetic fields on hybrid stars

Abstract

In this work we study the effects of strong magnetic fields on hybrid stars by using a full general-relativity approach, solving the coupled Maxwell-Einstein equation in a selfconsistent way. The magnetic field is assumed to be axi-symmetric and poloidal. We take into consideration the anisotropy of the energy-momentum tensor due to the magnetic field, magnetic field effects on equation of state, the interaction between matter and the magnetic field (magnetization), and the anomalous magnetic moment of the hadrons. The equation of state used is an extended hadronic and quark SU(3) non-linear realization of the sigma model that describes magnetized hybrid stars containing nucleons, hyperons and quarks. According to our results, the effects of the magnetization and the magnetic field on the EoS do not play an important role on global properties of these stars. On the other hand, the magnetic field causes the central density in these objects to be reduced, inducing major changes in the populated degrees of freedom and, potentially, converting a hybrid star into a hadronic star.

Magnetic Field and Neutron stars: A comprehensive study

“…where ε is the total energy density which is the sum of the matter energy density ε m and magnetic stress B 2 8π , P ⊥ and P are the perpendicular and parallel components of the total pressure with respect to the magnetic axis, P m is the matter pressure and MB is the magnetization. It has been previously shown [21,22,23] that the effect of landau quantization in the EoS is not significant for reasonable magnetic fields (although the magnetic field modifies significantly the central value of the EoS and population of the star [13]). The effect from magnetization can also as an approximation, be neglected.…”

“…The exact value of the magnetic field and its structure depend strongly on the region of the star in which the magnetic field is assumed to be found. This limit also needs to be calculated taking into account general relativity and magnetic field modifications in the metric, not to mention magnetic field modifications to the equation of state itself, which also has its central density substantially modified [13].…”

What can VLBI astrometry tell us about AR Sco?

“…A model-dependent distance of 116 ± 16 pc has been reported for AR Sco and the mass of the WD is in the range of 0.81 − 1.29 M (Marsh et al 2016). By using the observations of luminosity, the rotation frequency and the frequency derivative of the WD, Franzon & Schramm (2016) found that the WD might have a mass close to 1.29 M and estimated its radius of ∼ 4080 km and the central and surface magnetic fields of ∼ 0.9 × 10 13 G and ∼ 8.95 × 10 11 G, respectively. The parameters mentioned above are important for understanding the physical processes on-going in AR Sco, unfortunately, due to the relatively large uncertainty of distance (13%), they can not be tightly constrained.…”

“…Another aspect that will benefit from the distance determination is the amplitude estimation of the gravitational wave coming from AR Sco, the pulsing WD-MD binary system. Using the model-dependent distance of ∼ 116 pc, the gravitational wave amplitude for AR Sco was estimated to be ∼ 10 − (22−23) (Franzon & Schramm 2016), which might lead to a detectable signal by LIGO and VIRGO. By applying more precise distance, the gravitational wave amplitude from AR Sco can be tightly constrained, which would help to optimize detecting strategy for the gravitational wave detectors.…”

QGP Theory: Prospects, Challenges & open Questions

“…Note, however, that this does not imply a conflict with the observed heavy stars, as the reduction of the stellar masses due to the condensation only takes place for strongly magnetized stars, when the magnetic field itself leads to an increase of the allowed star masses [24]. Recently, there has been discussion involving the systematics of calculations of neutron star radii of typical 1.4 solar mass stars.…”