Unified description of astrophysical properties of neutron stars independent of the equation of state

Abstract

In recent years, a lot of work was done that has revealed some very interesting properties of neutron stars. One can relate the first few multipole moments of a neutron star, or quantities that can be derived from them, with relations that are independent of the equation of state (EoS). This is a very significant result that has great implications for the description of neutron stars and in particular for the description of the spacetime around them. Additionally, it was recently shown that there is a four parameter analytic spacetime, known as the two-soliton spacetime, which can accurately capture the properties of the geometry around neutron stars. This allows for the possibility of describing in a unified formalism the astrophysically relevant properties of the spacetime around a neutron star independently of the particulars of the EoS for the matter of the star. More precisely, the description of these astrophysical properties is done using an EoS omniscient spacetime that can describe the exterior of any neutron star. In the present work we investigate properties such as the location of the innermost stable circular orbit $R_{ISCO}$ (or the surface of the star when the latter overcomes the former), the various frequencies of perturbed circular equatorial geodesics, the efficiency of an accretion disc, its temperature distribution, and other properties associated with the emitted radiation from the disc, in a way that holds for all possible choices of a realistic EoS for the neutron star. Furthermore, we provide proof of principle that if one were to measure the right combinations of pairs of these properties, with the additional knowledge of the mass of the neutron star, one could determine the EoS of the star.

21 pages, 22 figures

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• Gravitational waves from f-modes excited by the inspiral of highly eccentric neutron star binaries
• A new method to constrain neutron star structure from quasi-periodic oscillations
• Orbital and epicyclic frequencies around neutron and strange stars in $R^2$ gravity
• Universal Relations and Alternative Gravity Theories
• An accurate metric for the spacetime around neutron stars
• Multipole moments and universal relations for scalarized neutron stars
• Accretion disks around neutron and strange stars in ${\mathcal{R}}^2$ gravity
• The I-Love-Q Relations for Superfluid Neutron Stars
• Universal relations for innermost stable circular orbits around rapidly rotating neutron stars
• Epicyclic oscillations in the Hartle-Thorne external geometry
• Universal Relations for rapidly rotating neutron stars using supervised machine-learning techniques
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• Innermost stable circular orbits of neutron stars in dilatonic-Einstein-Gauss-Bonnet theory
• Accretion tori around rotating neutron stars II: Oscillations and precessions
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