Effect of symmetry energy on properties of rapidly rotating neutron stars and universal relations

Effect of symmetry energy on properties of rapidly rotating neutron stars and universal relations
Pion Sudarshan Yeasin, Stefanos Tsiopelas, Armen Sedrakian, Jia-Jie Li
arXiv:2507.01093v1 Announce Type: new
Abstract: We investigated universal relations for compact stars rotating at the Keplerian (mass-shedding) limit, which is
highly relevant for understanding the rapidly rotating objects formed in the aftermath of a neutron star-neutron
star merger. Our analysis is based on a set of nucleonic EoS featuring systematic variations in the symmetry
energy slope parameter $L_{rm sym}$ and the isoscalar skewness parameter $Q_{rm sat}$, varied within ranges
that are broadly consistent with current laboratory and astrophysical constraints. The global observable
properties of isolated maximally rotating stars are examined, focusing on the mass-radius relation,
moment of inertia, quadrupole moment, and the Keplerian (maximum) rotation frequency, as well as their
variations in the $L_{rm sym}$-$Q_{rm sat}$ parameter space. Next, we demonstrate that, in the limit of Keplerian
rotation, universal relations remain valid across the same set of EoSs characterized by varying $L_{rm sym}$ and $Q_{rm sat}$.
In particular, we present explicit results for the moment of inertia and quadrupole moment as functions of compactness,
as well as for the moment of inertia – quadrupole moment relation. All of these relations exhibit excellent universality,
with deviations typically within a few percent and rarely exceeding 10% across a wide range of parameters.
These findings support the applicability of $I$-Love-$Q$-type universal relations in observational modeling
of maximally rotating compact stars and the gravitational wave emitted by them, when accounting for significant
variation in the symmetry energy and high-density behavior of the nuclear EoS.arXiv:2507.01093v1 Announce Type: new
Abstract: We investigated universal relations for compact stars rotating at the Keplerian (mass-shedding) limit, which is
highly relevant for understanding the rapidly rotating objects formed in the aftermath of a neutron star-neutron
star merger. Our analysis is based on a set of nucleonic EoS featuring systematic variations in the symmetry
energy slope parameter $L_{rm sym}$ and the isoscalar skewness parameter $Q_{rm sat}$, varied within ranges
that are broadly consistent with current laboratory and astrophysical constraints. The global observable
properties of isolated maximally rotating stars are examined, focusing on the mass-radius relation,
moment of inertia, quadrupole moment, and the Keplerian (maximum) rotation frequency, as well as their
variations in the $L_{rm sym}$-$Q_{rm sat}$ parameter space. Next, we demonstrate that, in the limit of Keplerian
rotation, universal relations remain valid across the same set of EoSs characterized by varying $L_{rm sym}$ and $Q_{rm sat}$.
In particular, we present explicit results for the moment of inertia and quadrupole moment as functions of compactness,
as well as for the moment of inertia – quadrupole moment relation. All of these relations exhibit excellent universality,
with deviations typically within a few percent and rarely exceeding 10% across a wide range of parameters.
These findings support the applicability of $I$-Love-$Q$-type universal relations in observational modeling
of maximally rotating compact stars and the gravitational wave emitted by them, when accounting for significant
variation in the symmetry energy and high-density behavior of the nuclear EoS.