Astrophysics of gravitational-wave sources


Glossary

The LISA detector is a spaceborne mission that will fly to space sometime in the 2030’s. It is expected to detect thousands of signals, among which we hope to find a handful of extreme-mass-ratio inspirals (EMRIs).

EMRIs are binaries in which one compact object is much more massive than the companion. With the LISA detector, we may observe the inspiral of a stellar-mass compact object onto a supermassive black hole (SMBH). These act as probes of the environments or any potential deviations to general relativity in the vicinity of the massive black hole.

For instance, EMRI observations could detect the presence of dark-matter (DM) spikes, namely overdensities in the distribution of galactic DM halos. This line of work has implications for detecting or constraining new Physics beyond the Standard Model.

The LISA mission will also unravel thousands of white-dwarf binaries in our very own galaxy. Some of these sources are loud enough to have already been detected with electromagnetic astrophysics. The loudness of these binaries could help explore the environments of the Milky Way, or reveal any modifications to gravity.


Projects

We have modelled with a fully relativistic treatment the DM spikes that are expected to grow adiabatically under the influence of the galaxy’s SMBH. We have estimated whether relativistic corrections to the spike or the dynamical friction drag they cause are important for observations of EMRIs within a DM cloud.

Paper

We have explored the effect of the accretion disks surrounding SMBHs at the centre of most galaxies, focussing on a phenomenon known as planetary-type migration. We have concluded that, for a large portion of the disks’ parameter space, EMRIs could be used to directly probe accretion properties and distinguish between competing effects. The disk’s viscosity could also be measured with appropriate electromagnetic counterparts. The analysis is generic enough to carry over to any environmental effect for which the torque can be written as a power law.

Paper

We have investigated whether galactic binaries in the Milky Way could be used to test modifications to gravity, such as those that predict a time dependence to the gravitational constant. We also provide constraints for inspiraling binaries for both the LISA and DECIGO-like missions.

Paper