Physics

Gravitational wave observations have unveiled the population of merging black holes and neutron stars, providing direct access to strong-field gravity and dense nuclear matter. These compact binaries emit gravitational radiation as they inspiral and merge, producing waveforms that encode: the masses and spins of the constituents, neutron star's equation of state, the properties of gravity in extreme regimes, and details of their astrophysical environments. Extracting this information requires precise theoretical predictions for comparison with observations. Next-generation detectors, both ground and space-based, are expected to observe 10^3-10^5+ cycles of a given binary merger, with potentially many thousands of events per year across disparate regimes of masses, eccentricities, etc. At this scale, numerical relativity simulations alone become computationally prohibitive, making precision analytical calculations essential.

In this talk I will present new analytical approaches to the gravitational two-body problem that combine effective field theory techniques from particle physics together with tools from General Relativity. I will discuss methods for computing the dynamics of isolated binaries at high perturbative orders, as well as methods for describing binaries embedded in gaseous or dark matter environments where environmental effects modify the orbital evolution and gravitational wave signal.

The calm of the quiescent sky is regularly interrupted by bursts of light that can outshine the entire galaxy. These powerful explosions are associated with mergers of compact objects, the collapse of stars, and rapidly accreting black holes, where gravitational binding energy is released and efficiently converted into radiation. The advent of electromagnetic time-domain surveys, high-energy telescopes, and gravitational-wave detectors is unveiling how matter works at these extreme conditions, offering insight into fundamental questions such as: How do compact objects form and acquire their magnetic fields? Which mechanisms launch outflows and jets? What determines the nature of the remnants they leave behind?  What are the main sites of heavy-element production?

Pulsar timing arrays (PTAs) consist of a set of regularly monitored millisecond pulsars with extremely stable rotational periods that are used as precise cosmic clocks. The arrival time of pulses can be altered by the passage of gravitational waves (GWs) between them and the Earth, thus serving as a galaxy-wide GW detector. Evidence for low-frequency (~nHz) gravitational waves has recently been reported for the first time across multiple PTA collaborations, opening a new observational window into the Universe. I will discuss how pulsar observations are used to measure GWs, what we are currently learning by mapping the nanohertz GW sky, and what lies ahead following a first detection.