Quadrupole moments of rotating neutron stars and strange stars

Abstract

We present results for models of neutron stars and strange stars constructed using the Hartle-Thorne slow-rotation method with a wide range of equations of state, focusing on the values obtained for the angular momentum $J$ and the quadrupole moment $Q$, when the gravitational mass $M$ and the rotational frequency $\Omega$ are specified. Building on previous work, which showed surprising uniformity in the behaviour of the moment of inertia for neutron-star models constructed with widely-different equations of state, we find similar uniformity for the quadrupole moment. These two quantities, together with the mass, are fundamental for determining the vacuum space-time outside neutron stars. We study particularly the dimensionless combination of parameters $QM/J^2$ (using units for which $c=G=1$). This quantity goes to 1 in the case of a Kerr-metric black hole and deviations away from 1 then characterize the difference between neutron-star and black-hole space-times. It is found that $QM/J^2$ for both neutron stars and strange stars decreases with increasing mass, for a given equation of state, reaching a value of around 2 (or even less) for maximum-mass models, meaning that their external space-time is then rather well approximated by the Kerr metric. If $QM/J^2$ is plotter against compactness $R/2M$ (where $R$ is the radius), it is found that the relationship is nearly unique for neutron-star models, independent of the equation of state, while it is significantly different for strange stars. This gives a new way of possibly distinguishing between them.

11 pages, 6 figures. Submitted to MNRAS

References in corpus (11)

• Shapiro delay measurement of a two solar mass neutron star
• A Massive Pulsar in a Compact Relativistic Binary
• The ATNF Pulsar Catalogue
• Neutron Star Observations: Prognosis for Equation of State Constraints
• Astrophysical Measurement of the Equation of State of Neutron Star Matter
• On mass-constraints implied by the relativistic precession model of twin-peak quasi-periodic oscillations in Circinus X-1
• Mass-angular-momentum relations implied by models of twin peak quasi-periodic oscillations
• The Hartle-Thorne circular geodesics
• Approximate analytic expressions for circular orbits around rapidly rotating compact stars
• The quadrupole moment of slowly rotating fluid balls
• Rotational parameters of strange stars in comparison with neutron stars

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