Eventi del Dottorato

Dottorato in Fisica

Journal Club Seminari 2021

08/03/2021   ore 16:00
in modalita' telematica

ore 16:00Raul Ciancarella
Tidal defirmability of exotic compact objects Introduction to xAct
1) The equation of state of neutron star matter leaves a clean imprint on the gravitational-wave signal emitted by inspiraling binary neutron stars. This imprint depends on the tidal deformability parameter of the neutron stars involved: measurements of such parameter can therefore directly constrain the neutron star equation of state. This theoretical framework of may be applied by extension to exotic objects with density and gravitational behaviour similar to neutron stars. More specifically, two kind of exotic Neutron Stars: one in which we allow them to present anisotropies in the internal pressure, and a second one in which we allow them to contain mirror dark matter. We will obtain the equilibrium sequences for both classes of exotic neutron stars, thus determining the maximum mass and the compactness as a functionof the mass.
We compare our results to the maximum mass constraint imposed by PSR J0348+0432 and to the GW170817 constraint on the tidal deformability. We bare able to find exotic neutron star configurations that can satisfy both constraints, despite using an equation of state that violates one of the constraints if one considers canonical neutron star models. We also quantify the deviations of our exotic neutron star models from the universal behaviour found in that links compactness and tidal deformability. We show that deviations from this universal behaviour can be significant, particularly in the presence of mirror dark matter. This highlights that when one interprets observations by using universal relations, one must be well aware of their realm of applicability.

XAct is a powerful tools in Mathematica that can perform abstract tensor calcolous and can be useful in perturbation theory (xPert) or in cosmology (xPand). We will present some basic functions and show a minimal example in wich we will find the Einstein Fiel Equation of a perturbed spherical metric.

ore 16:45Andrea Gnarini
Magneto-thermal evolution and X-ray emission of neutron stars: a 3D approach
1)Neutron stars (NSs) harbor extremely strong magnetic fields within their solid crust, they are born very hot and cool down as they age. Their thermal evolution is inherently coupled to that of their magnetic field. Knowledge of the secular magneto-thermal evolution can discriminate between different cooling scenarios when compared to observations, thus constraining the equation of state of ultra-dense matter.
The aim of this study is to model the evolution of the temperature and the magnetic field in the NS crust by means of numerical simulations performed with PARODY, a 3D, pseudo-spectral code which solves the coupled induction and temperature equations in the crust of an highly-magnetised isolated NS. A fully 3D approach is required in order to treat non-axysimmetric magnetic configurations and to explore small-scale structures which naturally arise as a consequence of the Hall term.
Moreover, in a NS the thermal map is shaped by the magnetic field topology, since heat flows in the crust mostly along the magnetic field lines. Self-consistent surface thermal maps can hence be produced by simulating the coupled magnetic and thermal evolution of the star to model the X-ray emission from the NS surface, deriving the spectrum and the pulse profile as seen by an observer at infinity, accounting for general-relativistic effects.


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