Sam Lander, who recently obtained his PhD from the University of Southampton, has arrived at the AEI to work with us for three months. He will be continuing his study of the stability of magnetic fields in neutron star spacetimes using perturbative techniques.
We are very happy to welcome Abraham Harte to the group as a postdoc working on vacuum Numerical Relativity. Abraham joins us from the University of Chicago where he worked on models for the “bobbing” and kicks of binary black hole systems. He will bring his analytical knowledge and expertise to interpret numerical binary black hole spacetimes.
Daniela Alic, Luciano Rezzolla, Ian Hinder and Philipp Mösta have released a new preprint on Dynamical damping terms for symmetry-seeking shift conditions.
Suitable gauge conditions are fundamental for stable and accurate numerical-relativity simulations of inspiralling compact binaries. A number of well-studied conditions have been developed over the last decade for both the lapse and the shift and these have been successfully used both in vacuum and non-vacuum spacetimes when simulating binaries with comparable masses. At the same time, recent evidence has emerged that the standard “Gamma-driver” shift condition requires a careful and non-trivial tuning of its parameters to ensure long-term stable evolutions of unequal-mass binaries. We present a novel gauge condition in which the damping constant is promoted to be a dynamical variable and the solution of an evolution equation. We show that this choice removes the need for special tuning and provides a shift damping term which is free of instabilities in our simulations and dynamically adapts to the individual positions and masses of the binary black-hole system. Our gauge condition also reduces the variations in the coordinate size of the apparent horizon of the larger black hole and could therefore be useful when simulating binaries with very small mass ratios.