Harvard-Smithsonian Center for Astrophysics
The phenomenology of AGN and quasars is extremely complex. Yet most of these features arise well within the sphere of influence of the black hole, where almost all information about the host galaxy is lost, so quasars should be simple. I review a series of fairly recent results that suggest that quasars are in fact simple, and that we have been confused by peripheral effects, mainly obscuration and host galaxy emission. Once accounted for, the entire continuum, from radio through the IR/optical/UV to the X-rays, is tightly coupled ,and so deterministic. Even the atomic features are well-behaved This gives hope that we can soon understand the processes at work and so have a predictive physical model of quasars. An example of a model that fits one part of that puzzle will be presented.
The recent direct observation of gravitational waves (GW) from merging black holes opens up the possibility of testing the theory of gravity in the strong regime at an unprecedented level. It is therefore interesting to explore which extensions to General Relativity (GR) could be detected. We construct an Effective Field Theory satisfying the following requirements. It is testable with GW observations; it is consistent with other experiments, including short distance tests of GR; it agrees with widely accepted principles of physics, such as locality, causality and unitarity; and it does not involve new light degrees of freedom. The most general theory satisfying these requirements corresponds to adding to the GR Lagrangian operators constructed out of powers of the Riemann tensor, suppressed by a scale comparable to the curvature of the observed merging binaries. The presence of these operators modifies the gravitational potential between the compact objects, as well as their effective mass and current quadrupoles, ultimately correcting the waveform of the emitted GW.