Dynamically stable ergostars exist: General relativistic models and simulations

Abstract

We construct the first dynamically stable ergostars (equilibrium neutron stars that contain an ergoregion) for a compressible, causal equation of state. We demonstrate their stability by evolving both strict and perturbed equilibrium configurations in full general relativity for over a hundred dynamical timescales ($\gtrsim 30$ rotational periods) and observing their stationary behavior. This stability is in contrast to earlier models which prove radially unstable to collapse. Our solutions are highly differentially rotating hypermassive neutron stars with a corresponding spherical compaction of $C=0.3$. Such ergostars can provide new insights into the geometry of spacetimes around highly compact, rotating objects and on the equation of state at supranuclear densities. Ergostars may form as remnants of extreme binary neutron star mergers and possibly provide another mechanism for powering short gamma-ray bursts.

arXiv comment5 pages, 3 figures, to appear in PRL

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• Jetlike structures in low-mass binary neutron star merger remnants
• The fate of twin stars on the unstable branch: implications for the formation of twin stars
• Locating ergostar models in parameter space
• Magnetic Ergostars, Jet Formation and Gamma-Ray Bursts: Ergoregions versus Horizons
• Equilibriums of extremely magnetized compact stars with force-free magnetotunnels
• Energy bounds and ergoregion instability in Einstein-Maxwell-Scalar field models
• Ergoregion instability in bosonic stars: scalar mode structure, universality, and weakly nonlinear effects
• Fully general-relativistic simulations of isolated and binary strange quark stars
• Nonlinear evolution of the ergoregion instability: Turbulence, bursts of radiation, and black hole formation