Axisymmetric Hydrodynamics in Numerical Relativity Using a Multipatch Method
Jerred Jesse, Matthew D. Duez, Francois Foucart, Milad Haddadi, Alexander L. Knight, Courtney L. Cadenhead, Francois Hebert, Lawrence E. Kidder, Harald P. Pfeiffer, Mark A. Scheel
We describe a method of implementing the axisymmetric evolution of general-relativistic hydrodynamics and magnetohydrodynamics through modification of a multipatch grid scheme. In order to ease the computational requirements required to evolve the post-merger phase of systems involving binary compact massive objects in numerical relativity, it is often beneficial to take advantage of these system's tendency to rapidly settle into states that are nearly axisymmetric, allowing for 2D evolution of secular timescales. We implement this scheme in the spectral Einstein code and show the results of application of this method to four test systems including viscosity, magnetic fields, and neutrino radiation transport. Our results show that this method can be used to quickly allow already existing 3D infrastructure that makes use of local coordinate system transformations to be made to run in axisymmetric 2D with the flexible grid creation capabilities of multipatch methods. Our code tests include a simple model of a binary neutron star postmerger remnant, for which we confirm the formation of a massive torus which is a promising source of post-merger ejecta.
The intrinsic derivative and centrifugal forces in general relativity: II. Applications to circular orbits in some familiar stationary axisymmetric spacetimes
A new numerical scheme to compute 3D configurations of quasiequilibrium compact stars in general relativity -- Application to synchronously rotating binary star systems --
We consider the equations for the coefficients of stationary rotating axisymmetric metrics governed by the Einstein-Euler equations, that is, the Einstein equations together with the energy-momentum tensor of a barotropic perfect fluid. Although the derived equations are not already known except for the case of the constant angular velocity described in the corotating coordinate system, the main content of this article is not to derive the equations, but to prove the equivalence of the derived equations with the full set of the Einstein equations, and to prove the consistency of the derived eq…
Quasi-equilibrium models of uniformly rotating axisymmetric and triaxial quark stars are computed in general relativistic gravity scenario. The Isenberg-Wilson-Mathews (IWM) formulation is employed and the Compact Object CALculator (COCAL) code is extended to treat rotating stars with finite surface density and new equations of state (EOSs). Besides the MIT bag model for quark matter which is composed of de-confined quarks, we examine a new EOS proposed by Lai and Xu that is based on quark clustering and results in a stiff EOS that can support masses up to $3.3M_\odot$ in the case we considere…
Gravitational waves from core collapse of rotating very-massive stars: 3D numerical relativity computation
The Pennsylvania State University（宾夕法尼亚州立大学）；Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut)（马克斯·普朗克引力物理学研究所（阿尔伯特·爱因斯坦研究所））；Kyoto University（京都大学）；Tohoku University（东北大学）
Dynamical axisymmetric compact objects in General Relativity
Arnold Sommerfeld Center for Theoretical Physics（阿诺德·索末菲理论物理中心）；Univ Lyon, CNRS, ENS de Lyon, Laboratoire de Physique (LPENSL)（里昂大学、法国国家科学研究中心、里昂高等师范学校、物理实验室）；Sede Esmeralda, Universidad de Tarapacá（塔拉帕卡大学埃斯梅尔达校区）；Instituto de Matemáticas, Universidad de Talca（塔尔卡大学数学研究所）
General relativity probably is not the definitive theory of gravity, due a number or issues, both from the theoretical and from the observational point of view. Alternative theories of gravity were conceived to extend general relativity and account for such issues. Among the most promising ones are scalar-tensor theories, which predict an enrichment of the phenomenology of compact objects, like neutron stars. We updated the well-tested XNS code to numerically solve the Einstein-Maxwell equations for a stationary, magnetised neutron star in a class of scalar-tensor theories containing the spont…
We formulate axisymmetric general relativity in terms of real Ashtekar--Barbero variables. We study the constraints and equations of motion and show how the Kerr, Schwarzschild and Minkowski solutions arise. We also discuss boundary conditions. This opens the possibility of a midisuperspace quantization using loop quantum gravity techniques for spacetimes with axial symmetry and time dependence.
In classical numerical relativity, marginally outer trapped surfaces (MOTSs) are the main tool to locate and characterize black holes. For five decades it has been known that during a binary merger, a new outer horizon forms around the initial apparent horizons of the individual holes once they are sufficiently close together. However the ultimate fate of those initial horizons has remained a subject of speculation. Recent axisymmetric studies have shed new light on this process and this pair of papers essentially completes that line of research: we resolve the key features of the post-swallow…
In a previous paper we formulated axisymmetric general relativity in terms of real Ashtekar--Barbero variables. Here we proceed to quantize the theory. We are able to implement Thiemann's version of the Hamiltonian constraint. We discuss its action including the matrix elements and its solutions. This provides a 2+1 dimensional arena to test ideas for the dynamics of quantum gravity and opens the possibility of quantum studies of rotating black hole spacetimes.
In numerical relativity, spacetimes involving compact strongly gravitating objects are constructed as numerical solutions of Einstein's equations. Success of such a process strongly depends on the availability of appropriate coordinates, which are typically constructed dynamically. A very robust coordinate choice is a so-called moving puncture gauge, commonly used for numerical simulations of black hole spacetimes. Nevertheless it is known to fail for evolving near-critical Brill wave data. We construct a new `quasi-maximal' slicing condition and demonstrate that it exhibits better behavior fo…
Einstein's equations as a thermodynamic identity: The cases of stationary axisymmetric horizons and evolving spherically symmetric horizons
视界的引力动力学和热力学之间有一个有趣的类比。在广义相对论的情况下，以及更广泛的一类Lanczos-Lovelock引力理论的情况下，可以将任何球对称视界附近的场方程解释为热力学恒等式TdS = dE + PdV。我们进一步研究了这种方法，并将结果推广到广义相对论的背景下，两个更一般的情况下：（i）静态轴对称的地平线和（ii）时间依赖的演变地平线。在这两种情况下，爱因斯坦方程的近视界结构都可以表示为视界虚位移下的热力学恒等式。这一结果表明，引力动力学的热力学解释并不局限于球对称或静态的视野，而是相当普遍的性质，并表明引力和热力学之间更深层次的联系。
We describe a set of time evolution equations and its numerical implementation for the investigation of non-axisymmetric oscillations of rapidly rotating compact objects in full General Relativity, taking into account the contribution of a dynamic spacetime. We derive the perturbation equations for the spacetime in the Hilbert gauge, while the hydrodynamical evolution is based on perturbations of the energy-momentum tensor. In our numerical implementation, we use Kreiss-Oliger dissipation in order to achieve a stable time evolution. Our code features high accuracy at comparably low computation…
We extend a recently developed numerical code to obtain stationary, axisymmetric solutions that describe rotating black hole spacetimes in a wide class of modified theories of gravity. The code utilizes a relaxed Newton-Raphson method to solve the full nonlinear modified Einstein's Equations on a two-dimensional grid with a Newton polynomial finite difference scheme. We validate this code by considering static and axisymmetric black holes in General Relativity. We obtain rotating black hole solutions in scalar-Gauss-Bonnet gravity with a linear (linear scalar-Gauss-Bonnet) and an exponential (…
Among the possible extensions of General Relativity that have been put forward in order to address some long standing issues in our understanding of the Universe, Scalar-Tensor Theories have received a lot of attention for their simplicity. Interestingly, some of these predict a potentially observable non-linear phenomenon, known as \textit{spontaneous scalarisation}, in the presence of highly compact matter distributions, like the case of neutron stars. Neutron stars are ideal laboratories to investigate the properties of matter under extreme conditions, and in particular they are known to ha…
