Nonlinear evolution of the r-modes in neutron stars.
TL;DR: The evolution of a neutron-star r-mode driven unstable by gravitational radiation is studied here using numerical solutions of the full nonlinear fluid equations to study the nonlinear evolution of the mode.
Abstract: The evolution of a neutron-star $r$-mode driven unstable by gravitational radiation is studied here using numerical solutions of the full nonlinear fluid equations. The dimensionless amplitude of the mode grows to order unity before strong shocks develop which quickly damp the mode. In this simulation the star loses about $40%$ of its initial angular momentum and $50%$ of its rotational kinetic energy before the mode is damped. The nonlinear evolution causes the fluid to develop strong differential rotation which is concentrated near the surface and poles of the star.
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01 Jan 2004
TL;DR: In this paper, it was shown that when only hydrodynamic instabilities (shear, Eddington-Sweet, etc.) are included in the calculation, one obtains neutron stars spinning at close to critical rotation at their surface.
Abstract: Rotation in massive stars has been studied on the main sequence and during helium burning for decades, but only recently have realistic numerical simulations followed the transport of angular momentum that occurs during more advanced stages of evolution. The results affect such interesting issues as whether rotation is important to the explosion mechanism, whether supernovae are strong sources of gravitational radiation, the star's nucleosynthesis, and the initial rotation rate of neutron stars and black holes. We find that when only hydrodynamic instabilities (shear, Eddington-Sweet, etc.) are included in the calculation, one obtains neutron stars spinning at close to critical rotation at their surface -- or even formally in excess of critical. When recent estimates of magnetic torques (Spruit 2002) are added, however, the evolved cores spin about an order of magnitude slower. This is still more angular momentum than observed in young pulsars, but too slow for the collapsar model for gamma-ray bursts.
60 citations
TL;DR: In this article, the authors study the bulk viscosity of dense matter, taking into account nonlinear effects that arise in the large amplitude'supra-thermal' region where the deviation of the chemical potentials from chemical equilibrium fulfills.
Abstract: We study the bulk viscosity of dense matter, taking into account nonlinear effects that arise in the large amplitude 'supra-thermal' region where the deviation of the chemical potentials from chemical equilibrium fulfills . This regime is relevant to unstable modes, such as r-modes, which grow in amplitude until saturated by nonlinear effects. We study the damping due to direct and modified Urca processes in hadronic matter, and due to non-leptonic weak interactions in strange quark matter. We give general results valid for an arbitrary equation of state of dense matter and find that the viscosity can be strongly enhanced by supra-thermal effects. Our study confirms previous results on quark matter and shows that the nonlinear enhancement is even stronger in the case of hadronic matter. Our results can be applied to calculations of the r-mode-induced spin-down of fast-rotating neutron stars, where the spin-down time will depend on the saturation amplitude of the r-mode.
54 citations
TL;DR: In this paper, it was shown that the most luminous supernova discovered very recently, ASASSN-15lh, could have been powered by a newborn ultra-strongly-magnetized pulsar, which initially rotates near the Kepler limit.
Abstract: In this paper we show that the most luminous supernova discovered very recently, ASASSN-15lh, could have been powered by a newborn ultra-strongly-magnetized pulsar, which initially rotates near the Kepler limit. We find that if this pulsar is a neutron star, its rotational energy could be quickly lost as a result of gravitational-radiation-driven r-mode instability; if it is a strange quark star, however, this instability is highly suppressed due to a large bulk viscosity associated with the nonleptonic weak interaction among quarks and thus most of its rotational energy could be extracted to drive ASASSN-15lh. Therefore, we conclude that such an ultra-energetic supernova provides a possible signature for the birth of a strange quark star.
54 citations
Cites methods from "Nonlinear evolution of the r-modes ..."
...This order is supported by numerical simulations (Stergioulas & Font 2001; Lindblom et al. 2001)....
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TL;DR: In this article, the authors analyzed the viscous damping of r-mode oscillations of compact stars, taking into account non-linear viscous effects in the large-amplitude regime.
Abstract: We analyze the viscous damping of r-mode oscillations of compact stars, taking into account non-linear viscous effects in the large-amplitude regime. The qualitatively different cases of hadronic stars, strange quark stars, and hybrid stars are studied. We calculate the viscous damping times of r-modes, obtaining numerical results and also general approximate analytic expressions that explicitly exhibit the dependence on the parameters that are relevant for a future spindown evolution calculation. The strongly enhanced damping of large amplitude oscillations leads to damping times that are considerably lower than those obtained when the amplitude dependence of the viscosity is neglected. Consequently, large-amplitude viscous damping competes with the gravitational instability at all physical frequencies and could stop the r-mode growth in case this is not done before by non-linear hydrodynamic mechanisms.
54 citations
Cites background from "Nonlinear evolution of the r-modes ..."
...Previously, various mechanisms for the large-amplitude behavior of r-modes have been suggested [6]....
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...Explicit numerical analyses of the general relativistic hydrodynamical equations [6, 9, 10] would present the ideal way to study the saturation and star evolution....
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TL;DR: In this article, the authors describe computational tools that have been developed to simulate dynamical mass transfer in semidetached, polytropic binaries that are initially executing synchronous rotation upon circular orbits.
Abstract: We describe computational tools that have been developed to simulate dynamical mass transfer in semidetached, polytropic binaries that are initially executing synchronous rotation upon circular orbits. Initial equilibrium models are generated with a self-consistent field algorithm; models are then evolved in time with a parallel, explicit, Eulerian hydrodynamics code with no assumptions made about the symmetry of the system. Poisson's equation is solved along with the equations of ideal fluid mechanics to allow us to treat the nonlinear tidal distortion of the components in a fully self-consistent manner. We present results from several standard numerical experiments that have been conducted to assess the general viability and validity of our tools, and from benchmark simulations that follow the evolution of two detached systems through five full orbits (up to approximately 90 stellar dynamical times). These benchmark runs allow us to gauge the level of quantitative accuracy with which simulations of semidetached systems can be performed using presently available computing resources. We find that we should be able to resolve mass transfer at levels /M > few × 10-5 per orbit through approximately 20 orbits with each orbit taking about 30 hours of computing time on parallel computing platforms.
53 citations