Locating ergostar models in parameter space

Abstract

Recently, we have shown that dynamically stable ergostar solutions (equilibrium neutron stars that contain an ergoregion) with a compressible and causal equation of state exist [A. Tsokaros, M. Ruiz, L. Sun, S. L. Shapiro, and K. Uryū, Phys. Rev. Lett. 123, 231103 (2019)]. These stars are hypermassive, differentially rotating, and highly compact. In this work, we make a systematic study of equilibrium models in order to locate the position of ergostars in parameter space. We adopt four equations of state that differ in the matching density of a maximally stiff core. By constructing a large number of models both with uniform and differential rotation of different degrees, we identify the parameters for which ergostars appear. We find that the most favorable conditions for the appearance of dynamically stable ergostars are a significant finite density close to the surface of the star (i.e., similar to self-bound quark stars) and a small degree of differential rotation.

8 pages, 3 figures. Matches published version

References in corpus (8)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• INTEGRAL Detection of the First Prompt Gamma-Ray Signal Coincident with the Gravitational Wave Event GW170817
• Constraints on a phenomenologically parameterized neutron-star equation of state
• Relativistic simulations of black hole-neutron star coalescence: the jet emerges
• On the stability and maximum mass of differentially rotating relativistic stars
• Modeling differential rotations of compact stars in equilibriums
• The role of the ergosphere in the Blandford-Znajek process
• Great Impostors: Extremely Compact, Merging Binary Neutron Stars in the Mass Gap Posing as Binary Black Holes

Cited by in corpus (8)

• Multimessenger Binary Mergers Containing Neutron Stars: Gravitational Waves, Jets, and $\mathbf{\gamma }$-Ray Bursts
• Models of binary neutron star remnants with tabulated equations of state
• Jetlike structures in low-mass binary neutron star merger remnants
• Accretion onto black holes inside neutron stars with piecewise-polytropic equations of state: analytic and numerical treatments
• Magnetic Ergostars, Jet Formation and Gamma-Ray Bursts: Ergoregions versus Horizons
• Ergoregion instability in bosonic stars: scalar mode structure, universality, and weakly nonlinear effects
• Energy bounds and ergoregion instability in Einstein-Maxwell-Scalar field models
• Nonlinear evolution of the ergoregion instability: Turbulence, bursts of radiation, and black hole formation