NADA: A new code for studying self-gravitating tori around black holes

TL;DR

NADA is a new two-dimensional numerical code that accurately simulates self-gravitating tori around black holes by solving Einstein and hydrodynamics equations with high-order methods and symmetry techniques.

Contribution

The paper introduces NADA, a novel 2D numerical code combining BSSN formulation, Cartoon method, and high-resolution shock-capturing schemes for studying self-gravitating accretion disks around black holes.

Findings

Validated code with tests on black hole evolutions and shock tubes.

Simulated black hole with self-gravitating torus in equilibrium.

Demonstrated code's accuracy and convergence.

Abstract

We present a new two-dimensional numerical code called Nada designed to solve the full Einstein equations coupled to the general relativistic hydrodynamics equations. The code is mainly intended for studies of self-gravitating accretion disks (or tori) around black holes, although it is also suitable for regular spacetimes. Concerning technical aspects the Einstein equations are formulated and solved in the code using a formulation of the standard 3+1 (ADM) system, the so-called BSSN approach. A key feature of the code is that derivative terms in the spacetime evolution equations are computed using a fourth-order centered finite difference approximation in conjunction with the Cartoon method to impose the axisymmetry condition under Cartesian coordinates (the choice in Nada), and the puncture/moving puncture approach to carry out black hole evolutions. Correspondingly, the general relativistic hydrodynamics equations are written in flux-conservative form and solved with high-resolution, shock-capturing schemes. We perform and discuss a number of tests to assess the accuracy and expected convergence of the code, namely (single) black hole evolutions, shock tubes, and evolutions of both spherical and rotating relativistic stars in equilibrium, the gravitational collapse of a spherical relativistic star leading to the formation of a black hole. In addition, paving the way for specific applications of the code, we also present results from fully general relativistic numerical simulations of a system formed by a black hole surrounded by a self-gravitating torus in equilibrium.