Constraining the electric charge of binary black holes and neutron stars through gravitational wave observations

Abstract

Gravitational wave observations provide new possibilities to explore the Universe. A promising area for gravitational wave physics is compact binary systems consisting of black holes or neutron stars. Both are generally expected to be electrically neutral to good approximation, however general relativity does not prohibit either to possess a net electric charge. Should there be a significant electric charge present in a binary system, this would influence the orbital motion and consequently be noticeable through gravitational wave analysis. In this thesis, we lay down the groundwork for gravitational waves from binary systems and motivate how electric charges can be accreted by black holes. We derive the additional energy and radiated power terms induced by the charges and determine how these influence the gravitational waveform. We find that there is a -1 post-Newtonian term that includes a relative electric charge difference and can only take on non-positive values. Furthermore, using data from five binary black hole events, we produce probability distributions of the -1 post-Newtonian term. None of the events show signs of a significant relative charge difference. We estimate 90% upper bounds on the dimensionless relative charge difference of the binaries which are all in the order of 10^-1. From here, we move on to the double pulsar PSR J0737-3039. Through radio observations, we again estimate an upper bound on the dimensionless relative charge difference, which turns out to be in the order of 10^-3. Finally, we adopt the Fisher matrix formalism to derive future bounds on black hole binaries that can potentially be reached once the Einstein Telescope becomes active.