We show that the r-mode instability can generate strong toroidal fields in the core of accreting millisecond quark stars by inducing differential rotation. We follow the spin frequency evolution on a long time scale taking into account the magnetic damping rate in the evolution equations of r-modes. The maximum spin frequency of the star is only marginally smaller than in the absence of the magnetic field. The late-time evolution of the stars which enter the r-mode instability region is instead rather different if the generated magnetic fields are taken into account: they leave the millisecond pulsar region and they become radio pulsars.
In millisecond pulsars the existence of the Coriolis force allows the development of the so-called Rossby oscillations (r-modes) which are know to be unstable to emission of gravitational waves. These instabilities are mainly damped by the viscosity of the star or by the existence of a strong magnetic field. A fraction of the observed millisecond pulsars are known to be inside Low Mass X-ray Binaries (LMXBs), systems in which a neutron star (or a black hole) is accreting from a donor whose mass is smaller than 1 $M_\odot$. Here we show that the r-mode instabilities can generate strong toroidal…
In rotating neutron stars the existence of the Coriolis force allows the presence of the so-called Rossby oscillations (r-modes) which are know to be unstable to emission of gravitational waves. Here, for the first time, we introduce the magnetic damping rate in the evolution equations of r-modes. We show that r-modes can generate very strong toroidal fields in the core of accreting millisecond pulsars by inducing differential rotation. We shortly discuss the instabilities of the generated magnetic field and its long time-scale evolution in order to clarify how the generated magnetic field can…
The outer crust properties of cold non-accreting neutron stars are studied within the framework of the quark-meson coupling (QMC) model, which includes the effects of modifications of the quark structure inside individual nucleons when they are within a high-density nuclear medium. With a unique set of five well-constrained adjustable parameters, which have a clear physical basis, the QMC model gives predictions for the ground state observables of even-even nuclei which agree with experiment as well as traditional models. Furthermore, it gives improved theoretical values for nuclei thought to …
Magnetic fields are important for accretion disc structure. Magnetic fields in a disc system may be transported with the accreted matter. They can be associated with either the central body and/or jet, and be fossil or dynamo excited in situ. We consider dynamo excitation of magnetic fields in accretion discs of accreting binary systems in an attempt to clarify possible configurations of dynamo generated magnetic fields. We first model the entire disc with realistic radial extent and thickness using an alpha-quenching non-linearity. We then study the simultaneous effect of feedback from the Lo…
We present here a phenomenological solid quark star pulsar model to interpret the observed thermal X-ray emission of isolated pulsars. The heat capacity for solid quark stars was found to be quite small, so that the residual internal stellar heat gained at the birth of the star could be dissipated in an extremely short timescale. However, the bombardment induced by backflowing plasma at the poles of solid quark stars would get the stars be reheated, so that long term soft X-ray emission can be sustained. Such a scenario could be used for those X-ray pulsars with significant magnetospheric acti…
In this paper, we have investigated the accreting millisecond X-ray pulsars, which are rapidly rotating neutron stars in low-mass X-ray binaries. These systems show coherent X-ray pulsations that arise when the accretion flow is magnetically channeled to the stellar surface. Here, we have developed the fundamental equations for an accretion disc around accreting millisecond X-ray pulsars in the presence of a dynamo generated magnetic fields in the inner part of the disc and we have also formulated the numerical method for the structure equations in the inner region of the disc and the highest …
Rotating supermassive black holes produce jets and their origin is connected to magnetic field that is generated by accreting matter flow. There is a point of view that electromagnetic fields around rotating black holes are brought to the hole by accretion. In this situation the prograde accreting disks produce weaker large-scale black hole threading magnetic fields, implying weaker jets that in retrograde regimes. The basic goal of this paper is to find the best candidates for retrograde accreting systems in observed active galactic nuclei. We show that active galactic nuclei with low Eddingt…
The flow of a matter, accreting onto a magnetized neutron star, is accompanied by an electric current. The closing of the electric current occurs in the crust of a neutron stars in the polar region across the magnetic field. But the conductivity of the crust along the magnetic field greatly exceeds the conductivity across the field, so the current penetrates deep into the crust down up to the super conducting core. The magnetic field, generated by the accretion current, increases greatly with the depth of penetration due to the Hall conductivity of the crust is also much larger than the transv…
For a set of equation of state (EoS) models involving interacting strange quark matter, characterized by an effective bag constant (B_eff) and a perturbative QCD corrections term (a_4), we construct fully general relativistic equilibrium sequences of rapidly spinning strange stars for the first time. Computation of such sequences is important to study millisecond pulsars and other fast spinning compact stars. Our EoS models can support a gravitational mass (M_G) and a spin frequency at least up to approximately 3.0 solar mass and approximately 1250 Hz respectively, and hence are fully consiste…
Context: Accretion-powered X-ray pulsars show highly energy-dependent and complex pulse-profile morphologies. Significant deviations from the average pulse profile can appear, in particular close to the cyclotron line energies. These deviations can be described as energy-dependent phase lags, that is, as energy-dependent shifts of main features in the pulse profile. Aims: Using a numerical study we explore the effect of cyclotron resonant scattering on observable, energy-resolved pulse profiles. Methods: We generated the observable emission as a function of spin phase, using Monte Carlo simula…
In this paper, we find the heat capacity of the magnetic dual chiral density wave (MDCDW) phase of dense quark matter and use it to explore the feasibility of this phase for a neutron star interior. MDCDW is a spatially inhomogeneous phase of quark matter known to be favored at intermediate densities over the chirally symmetric phase and the color-flavor-locked superconducting phase. By comparing our result to the lower limit of the core heat capacity established from observations of transiently accreting neutron stars, we show that the heat capacity of MDCDW quark matter is well above that lo…
We investigate an unique accreting millisecond pulsar with X-ray eclipses, SWIFT J1749.4$-$2807 (hereafter J1749), and try to limit the binary system by various methods including that of the Roche lobe, the mass-radius relations of both a main sequence (MS) and a white dwarf (WD) companion stars, as well as the measured mass function of the pulsar. The calculations are based on the assumption that the radius of the companion star has reached its Roche radius (or at 90%), but the pulsar's mass has not been assumed to be a certain value. Our results are as follows. The companion star should be a…
We explore heavy element nucleosynthesis in the explosion of massive stars which are triggered by a quark-hadron phase transition during the early post bounce phase of core-collapse supernovae. The present study is based on general relativistic radiation hydrodynamics simulations with three-flavor Boltzmann neutrino transport in spherical symmetry, which utilize a quark-hadron hybrid equation of state based on the MIT bag model for strange quark matter. The quark-hadron phase transition inside the stellar core forms a shock wave propagating towards the surface of the proto-neutron star. The sh…
Accretion disks around compact objects are expected to enter an unstable phase at high luminosity. One instability may occur when the radiation pressure generated by accretion modifies the disk viscosity, resulting in the cyclic depletion and refilling of the inner disk on short timescales. Such a scenario, however, has only been quantitatively verified for a single stellar-mass black hole. Although there are hints of these cycles in a few isolated cases, their apparent absence in the variable emission of most bright accreting neutron stars and black holes has been a lingering puzzle. Here we …
The origin of the spins of giant planets is an open question in astrophysics. As planets and stars accrete from discs, if the specific angular momentum accreted corresponds to that of a Keplerian orbit at the surface of the object, it is possible for planets and stars to be spun up to near-breakup speeds. However, accretion cannot proceed onto planets and stars in the same way that accretion proceeds through the disk. For example, the magneto-rotational instability cannot operate in the region between the nearly-Keplerian disk and more slowly-rotating surface because of the sign of the angular…
Dark matter effects on the properties of hybrid neutron stars
School of Mathematics and Physics, China University of Geosciences（中国地质大学数学与物理学院）；INFN, Sezione di Catania, Dipartimento di Fisica, Universitá di Catania（意大利国家核物理研究所卡塔尼亚分部卡塔尼亚大学物理系）
The presence of exotic hadrons, such as hyperons and $Δ$ isobars, in the dense nuclear matter in their cores has been shown to produce important changes in the properties of neutron stars. Within the quark-meson coupling model, we show that the many-body forces generated by the change in the internal quark structure of the baryons in the strong scalar mean fields generated in dense nuclear matter prohibit the appearance of $Δ$ isobars.
