hide
Free keywords:
Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE,General Relativity and Quantum Cosmology, gr-qc,Nuclear Theory, nucl-th
Abstract:
Universal relations that are insensitive to the equation of state (EoS) are
useful in reducing the parameter space when measuring global quantities of
neutron stars (NSs). In this paper, we reveal a new universal relation that
connects the eccentricity to the radius and moment of inertia of rotating NSs.
We demonstrate that the universality of this relation holds for both
conventional NSs and bare quark stars (QSs) in the slow rotation approximation,
albeit with different relations. The maximum relative deviation is
approximately $1\%$ for conventional NSs and $0.1\%$ for QSs. Additionally, we
show that the universality still exists for fast-rotating NSs if we use the
dimensionless spin to characterize their rotation. The new universal relation
will be a valuable tool to reduce the number of parameters used to describe the
shape and multipoles of rotating NSs, and it may also be used to infer the
eccentricity or moment of inertia of NSs in future X-ray observations.
