Extreme mass ratio inspirals

The theoretical work done in the gravity group focuses on calculating the waveforms of the gravitational radiation as emitted by Extreme Mass Ratio Inspirals (EMRI's): binary systems of stars in which one of the stars is very much heavier than the other. Such systems are expected to lead to a significant amount of gravitational waves, and accurate waveforms are therefore desired as input for data analysis.

Such waveforms have been well-known for a long time, in the special case the stars have low masses and/or they are far away from each other. However, in realistic scenarios, the stars can get very close and fully relativistic effects can no longer be ignored. It are these waves that are physically the most interesting, and waveforms for this sort of radiation is what our group is after.

This challenge consists of two parts. Firstly, the orbit of the smaller star needs to be determined, and for this we use a fundamentally new method: whereas other research groups calculate orbits numerically or by post-newtonian expansion, our group has devised a way to do it by an approximation method that does not compromise the full relativistic effects that come into play when the stars get very close to each other. Secondly, the gravitational waves that come from this orbit need to be calculated. For this, our group has written a  numerical code, closely following work by Martel & Poisson and Lousto & Price, that evaluates this in high resolution. 

The results are waveforms that closely resemble the purely numerical ones found in literature. As we expand our code, we plan to build in additional effects: energy losses due to the emission of gravitational waves, the conservative self force effect, and the effects of electromagnetic fields on the orbits of charged particles the former two will increase the accuracy of the orbits, whereas the latter of these can be of interest to astronomers.

The results will serve as templates for data analysists in our gravity group, hence bridging the gap between theory and experiment.