# Thorsten Kellermann

**Room:** 0.62

**Phone:** +49 (0) 331 567 7186

**Fax:** +49 (0) 331 567 7298

**email:** (@aei.mpg.de) thorsten.kellermann

## Research

As a member of the numerical relativity group my research covers two main parts. On the one hand I am developing new numerical methods to solve the equations which come up in the field of relativistic astrophysics. On the other hand I am looking for scenario which can be described with equations in ideal relativistic hydrodynamics in an axisymmetric approach.

## Improving numerical methods

In the first part of my PhD work, I developed an axisymmetric version of theĀ *Whisky Code *. During working out the formulations of relativistic hydrodynamics in cylindrical coordinates I realised, that there are two ways two ways to write down the equations. From a mathematical point of few the equations are equal, but from the numerical point of few the equations show different behaviour in the precision of the results an the convergence behaviour. A detailed analysis can be find the related publication (see below).

## Critical behaviour in relativistic hydrodynamics

Two colliding neutron stars can end up in a new neutron star or in a black hole. With the Whisky2D code I consider the head on collision of two equal neutron stars initial data. The initial data are part of a n-dimensional parameter space which includes e.g. speed, central density, parameter of the equation of state and so on. An investigation of the head on collision shows that the parameter space is divided in a part which results in a new neutron star and a part which results in a black hole. Furthermore there is an n-1 dimensional hyper surface between the two parts of parameter space. Taking initial data which are very close to the hyper surface produce after the merging of the two stars a metastable equilibrium. It means before the system come up with a stable neutron star or a black hole, there is a intermediate star. The life time of this metastable equilibrium is related to the aberration of the taken initial parameter to parameter which are on the hyper surface. A mathematical investigation of the problem shows, that initial data taken from the hyper surface produce an intermediate star with infinite life time.

In this project I am looking for parameter sets which are as close a possible to the metastable equilibrium. The goal is two figure out the physical properties of the system in the close the critical limit. Results could be use to figure out new upper limits of the occurrence of black holes.

Publications

Here is a link to my publications since 2000 (from Spires)