arXiv subjects

Elia Giliberti

Publications and source records attributed to Elia Giliberti.

7 recordsLinked to original sources

arXiv2026

Frozen-composition effects on rotational failure of neutron-star crusts

The elastic response of a neutron-star crust to rotational loading depends on whether weak interactions can restore chemical equilibrium during the deformation. We quantify this effect using unified equations of state and compare chemically equilibrated and frozen-composition responses within the same Newtonian hydro-elastic framework. Frozen composition increases the effective bulk modulus and redistributes the strain throughout the inner crust rather than producing a simple global rescaling. For BSk24, the breaking frequency decreases from $0.4997\Omega_K$ to $0.3912\Omega_K$, a reduction of 21.7 per cent, while the location of first failure moves to higher density. Comparable reductions are obtained for BSk21, whereas SLy4 gives a smaller effect of 16.7 per cent. For BSk24 the relative reduction remains close to 21--22 per cent over the mass range $1.2$--$2.0,M_\odot$. A density-resolved perturbation analysis shows that the result is controlled by the radial overlap between the microphysical frozen-composition stiffening and the mechanical susceptibility of the crust, with most of the linear sensitivity in the BSk models arising from $0.01<n_B<0.03,{\rm fm}^{-3}$. These results show that chemical non-equilibrium can substantially modify both the rotational failure threshold and the layer in which crustal failure begins.

astro-ph.SR↗

arXiv2026

Vortex pinning and the elastic response of neutron-star crusts II. Non-axisymmetric loading and Magnus mountains

Pinned superfluid vortices transmit a Magnus force to the neutron-star crust. A non-axisymmetric component of the superfluid-lattice lag can therefore support a persistent mass quadrupole. We calculate the l=m=2 response of self-gravitating, radially stratified spherical stars with SLy4 and BSk21 backgrounds, using a local microscopic pinning cap and a density-dependent Coulomb-lattice shear modulus. For a 1.4 M_sun star at 100 Hz, the equilibrium-compression maxima are epsilon=2.67x10^-9 (SLy4) and 2.44x10^-9 (BSk21). The global quadrupole is strikingly insensitive to the shear prescription: replacing mu=0.01P by the Coulomb profile and strongly varying uncertain edge layers changes the result only at the percent level. The dominant internal sensitivity is instead compressional. A density-resolved compressional kernel increases through the inner crust and steepens close to the crust-core interface, particularly for BSk21, showing that the deep inner crust controls the EoS dependence of the mountain. A fixed-composition calculation is used only as a non-relaxed sensitivity diagnostic, not as the secular prediction. At a common true local velocity benchmark, our fiducial ellipticities remain more than an order of magnitude below the complementary two-component cylindrical calculation of Gangwar & Jones (2026). We argue that the comparison points to the relative superfluid-lattice degree of freedom as the natural next ingredient for a common spherical model. The main result is therefore physical rather than numerical: the Magnus-mountain scale is robust to shear microphysics, while the deep-crust compressional response sets the leading uncertainty of the one-displacement model.

astro-ph.HE↗

arXiv2026

Vortex pinning and the elastic response of neutron-star crusts - I. Axisymmetric loading

Vortex pinning is central to the standard interpretation of pulsar glitches, but the mechanical load exerted by a pinned vortex array on the solid crust has received less attention than the angular-momentum reservoir itself. We calculate the axisymmetric elastic response of a continuously stratified neutron-star crust to this load using realistic SLy4 and BSk21 stellar backgrounds and composition-dependent Coulomb shear moduli. The superfluid-crust lag sets the Magnus force, while the mesoscopic pinning force of Seveso et al. (2016) provides a local upper bound. At low lag the response is linear; progressive local saturation then produces a broad transition and a finite high-lag envelope. The stress maximum is robustly located at the deep crustal boundary towards the rotation axis, although the local Magnus force vanishes on-axis, showing that the localization is produced by global elastic-gravitational redistribution. Realistic elasticity changes the stress amplitude by 10-20 per cent relative to the common mu=10^-2 P prescription and reverses the SLy4-BSk21 ordering. At a Vela-motivated lag of 10^-2 rad s^-1, the maximum strain is only 3.1 x 10^-5 (SLy4) and 4.7 x 10^-5 (BSk21), remaining below 1.4 x 10^-4 on the formal plateau. A 1.2-2.0 solar-mass scan changes the stress amplitude by only about 20 per cent and leaves the deep-polar localization unchanged. Pinning therefore supplies a structured and astrophysically relevant crustal pre-stress, but cannot by itself break an initially relaxed crust.

astro-ph.HE↗

arXiv2021

Starquakes in millisecond pulsars and gravitational waves emission

So far, only transient Gravitational waves (GWs) produced by catastrophic events of extra-galactic origin have been detected. However, it is generally believed that there should be also continuous sources of GWs within our galaxy, such as accreting neutron stars (NSs). In fact, in accreting NSs, centrifugal forces can be so strong to break the neutron star crust (causing a starquake), thus producing a quadrupole moment responsible for the continuous emission of GWs. At equilibrium, the angular momentum gained by accretion and lost via GWs emission should balance each other, stopping the stellar spin-up. We hereinafter investigate the above physical picture within the framework of a Newtonian model describing compressible, non-magnetized, and self-gravitating NSs. In particular, we calculate the rotational frequency need to break the stellar crust of an accreting pulsar and we estimate the upper limit for the ellipticity due to this event. Depending on the equation of state (EoS) and on the mass of the star, we calculated that the starquake-induced ellipticity ranges from $10^{-9}$ to $10^{-5}$. The corresponding equilibrium frequency that we find is in good agreement with observations and, for all the scenarios, it is below the observational limit frequency of $716.36$ Hz. Finally, we also discuss possible observational constraints on the ellipticity upper limit of accreting pulsars.

astro-ph.HE↗

arXiv2020

Modelling strains and stresses in continuously stratified rotating neutron stars

We introduce a Newtonian model for the deformations of a compressible, autogravitating, and continuously stratified neutron star. The present framework can be applied to a number of astrophysical scenarios as it allows us to account for a great variety of loading forces. In this first analysis, the model is used to study the impact of a frozen adiabatic index in the estimate of rotation-induced deformations: we assume a polytropic equation of state for the matter at equilibrium but, since chemical reactions may be slow, the perturbations with respect to the unstressed configuration are modelled by using a different adiabatic index. We quantify the impact of a departure of the adiabatic index from its equilibrium value on the stressed stellar configuration and we find that a small perturbation can cause large variations both in displacements and strains. As a first practical application, we estimate the strain developed between two large glitches in the Vela pulsar showing that, starting from an initial unstressed configuration, it is not possible to reach the breaking threshold of the crust, namely to trigger a starquake. In this sense, the hypothesis that starquakes could trigger the unpinning of superfluid vortices is challenged and, for the quake to be a possible trigger, the solid crust must never fully relax after a glitch, making the sequence of starquakes in a neutron star an history-dependent process.

astro-ph.HE↗

arXiv2019

Conceptualization of Electromagnetic Induction at various Educational Levels: a Case Study

A vast scientific literature in physics education documents a general widespread difficulty in dealing with Electro-Magnetic Induction (EMI) at various levels of instruction. But, at the best of our knowledge, there is a lack of research that compares difficulties about EMI at different educational degrees. We discuss here a case study about Italian high school, graduate students' and teacher's conceptualization of some aspects of EMI as a function of the sample instruction level. We analyse the answers to a multiple choice written questionnaire, adapted from the literature and given to a total of 49 students. Some difficulties, emerged during the exams of university students of a physics education course while discussing their final project concerning a didactical path about EMI for secondary school, are also discussed. We find that some deep misunderstandings are common at all levels of education and probably come from the very poor link, generally presented in teaching EMI, between the Faraday's flux law and the Lorentz force.

physics.ed-ph↗

arXiv2019

Incompressible analytical models for spinning-down pulsars

We study a class of Newtonian models for the deformations of non-magnetized neutron stars during their spin-down. The models have all an analytical solution, and thus allow to understand easily the dependence of the strain on the star's main physical quantities, such as radius, mass and crust thickness. In the first ``historical'' model the star is assumed to be comprised of a fluid core and an elastic crust with the same density. We compare the response of stars with different masses and equations of state to a decreasing centrifugal force, finding smaller deformations for heavier stars: the strain angle is peaked at the equator and turns out to be a decreasing function of the mass.We introduce a second, more refined, model in which the core and the crust have different densities and the gravitational potential of the deformed body is self-consistently accounted for. Also in this case the strain angle is a decreasing function of the stellar mass, but its maximum value is at the poles and is always larger than the corresponding one in the one-density model by a factor of two. Finally, within the present analytic approach, it is possible to estimate easily the impact of the Cowling approximation: neglecting the perturbations of the gravitational potential, the strain angle is 40\% of the one obtained with the complete model.

astro-ph.HE↗