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

Understand

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.