CoCoNuT is a general relativistic hydrodynamics code with dynamical space-time evolution. The main aim of this numerical code is the study of several astrophysical scenarios in which general relativity can play an important role, namely the collapse of rapidly rotating stellar cores and the evolution of isolated neutron stars.

The code has two flavors: CoCoA, the axisymmetric (2D) magnetized version, and CoCoNuT, the 3D non-magnetized version. The CoCoA project was started by Harald Dimmelmeier at the Max-Planck Institute for Astrophysics (Garching bei München, Germany) as part of his PhD thesis. It was extended to 3D (CoCoNuT) in collaboration with Jérôme Novak from the LUTH laboratory at the Observatoire de Paris (Meudon, France). This web page is intended to be a presentation of the numerical code and its scientific results. This code is not of public domain.

• 3+1 in Spherical polar coordinates:

  CoCoNuT uses the 3+1 decomposition of the Einstein equations in spherical polar coordinates. This coordinate system is very well adapted to the core collapse scenario and neutron star evolution for which the code is intended. It allows to reduce easily the dimensionality of the problem in axisymmetry (2D) and in spherical symmetry (1D).

• Godunov-type schemes:

  The use of conservative methods (approximate Riemann solvers) allows high accuracy in the preservation of global quantities as mass or momentum and the correct treatment of discontinuities during the evolution.

• CFC metric evolution:

  For the metric evolution the conformally flatness condition (CFC) approximation is used. This approximation has proven to be very powerful in the core collapse scenario with extraordinary good agreement with full general relativistic simulations.

• Mariage des Maillages:

  The system of CFC equations consist in a set of elliptic non-linear equations which are solved with spectral methods by means of the LORENE library developed at Meudon. The interface between the spectral grid for the metric and the finite differences grid for the hydrodynamics is performed by means of the "Mariage des Maillages" (grid wedding) technique.

• Microphysics:

  Several equations of state can be used during the evolution, from simple analytical expressions (polytropic, ideal gas, hybrid eos) to microphysical equations of state in tabulated form (SHEN, LSEOS). A parametrized deleptonization scheme allows a simplified neutrino treatment during the collapse.

• GRMHD:

  The axisymmetric version of the code (CoCoA) is able to solve the ideal magneto-hydrodynamics equations in general relativity. The code uses constrained transport scheme to preserve the solenoidal condition for the magnetic field. Furthermore it has the ability of recovering the primitives variables from the conserved ones with a robust procedure even in the case of microphysical equations of state.

The main contributors and maintainers to the CoCoNuT/CoCoA code are:

• Harald Dimmelmeier
• Jérôme Novak
• Pablo Cerdá-Durán

• Isabel Cordero-Carrión
• Ernazar B. Abdikamalov

CoCoNuT	= Core Collapse with "Nu" (=new) Technology
CoCoA	= Core Collapse in Axisymmetry