What happens when two masses scatter? This deceptively simple question has produced a series of surprises that touch on deep issues in general relativity, such as the localizability of gravitational field energy, the notion of asymptotic flatness at timelike infinity, and observability of particle position. Most recently, we found that the…

Abstract:

Guided by the principles of effective field theory, I will discuss three consecutive avenues to constrain physics beyond General Relativity with black-hole observations.

1) Shadows: Without specifying any particular gravitational dynamics, I will discuss image features of black-hole shadows in general…

Over last six years, the LIGO-Virgo detections of gravitational waves from compact binary mergers have underlined their promise as an independent and powerful tool to explore the Universe. Nevertheless, the electromagnetic observations of the counterparts of gravitational-wave sources provide different and complementary information about the…

In this talk, we introduce and solve the characteristic gluing problem for the Einstein vacuum equations. We prove that obstructions to characteristic gluing come from an infinite-dimensional space of conservation laws along null hypersurfaces for the linearized equations at Minkowski. We show that this obstruction space splits into an infinite…

Abstract: The AdS instability conjecture provides an example of weak turbulence appearing in the dynamics of the Einstein equations in the presence of a negative cosmological constant. The conjecture claims the existence of arbitrarily small perturbations to the initial data of Anti-de Sitter spacetime which, under evolution by the vacuum…

Abstract:

As was realized by Bondi, Metzner, van der Burg, and Sachs (BMS), the symmetry group of asymptotic infinity is not the Poincaré group, but an infinite-dimensional group called the BMS group. Because of this, understanding the BMS frame of the gravitational waves produced by numerical relativity is crucial for ensuring that…

Abstract: Over the past years, electromagnetic and gravitational observations have been used to understand the nature of compact objects and the matter around them. However, our ability to learn about the underlying fundamental physics depends heavily on our understanding of the theory of gravity that describes the geometry around these compact…

Gravitational waves from the coalescence of compact binaries provide a unique opportunity to test gravity in the strong field regime. In particular, the postmerger phase of the gravitational signal is a proxy for the nature of the remnant.

This is of particular interest in view of some quantum-gravity models which predict the…

During its ringdown phase a perturbed black-hole produces radiation at characteristic (complex) frequencies, much like the normal frequencies of a guitar string. These quasinormal frequencies carry information about the geometry of the black hole. In this talk I will review the problem of finding quasinormal frequencies, and discuss recent work…

The discovery of the quark-gluon plasma that forms in heavy-ion collision experiments provides a unique opportunity to study the properties of matter under extreme conditions, as the quark-gluon plasma is the hottest, smallest, and densest fluid known to humanity. Studying the quark-gluon plasma also provides a window into the earliest moments…

Gravitational waves transport information from faraway regions of the Universe. Since the first detection of gravitational waves by Advanced LIGO in September 2015, several other events have been recorded by the LIGO/VIRGO collaboration. In general relativity (GR), most studies so far have been devoted to sources like binary black hole mergers…

A priori it would be surprising if all low-luminosity supermassive black holes, such as those in the centers of M87 and our own galaxy, had accretion disks aligned with their spin. The combination of such misalignment with differential torques from the black hole results in rich dynamics that have not been fully explored in the literature,…

Abstract:

Recently, several examples of traversable wormholes supported by well-controlled quantum effects and respecting reasonable energy conditions have been constructed. In this talk, I will describe a generalization of such solutions involving more than two mouths in the same asymptotic region. These wormholes may be traversed…

Abstract: In this talk, I will provide an overview of theoretical models of black hole accretion aimed primarily at non-specialists. I will focus in particular on efforts to understand the dynamics of, and radiation from, plasma in the near-horizon environment, both analytically and using numerical simulations. I will discuss these results in…

Abstract:

Stellar theory predicts the existence of a black hole mass gap in the range ~50 to ~120 solar masses resulting from pair instability supernovae. The binary black holes of LIGO-Virgo's first two observing runs supported this prediction, showing evidence for a dearth of component black hole masses above 45 solar masses…

Abstract:

Black holes have long been known to possess an entropy proportional to their horizon area, and an important goal in quantum gravity is to characterize the microstates responsible for this entropy. One way to approach this task is to identify symmetries of the black hole under which the microstates are expected to transform…

In this talk we will investigate the past dynamics of cosmological solutions to Einstein's equations, containing a Big Bang singularity. More precisely, we will focus on the classical generalised Kasner examples. The celebrated "singularity'' theorem of Hawking states that the past of sufficiently small perturbations of such solutions are…

The observation of gravitational and electromagnetic waves from a binary neutron star (BNS) merger in August 2017 conveyed unique information on the nature of matter at supranuclear densities, on the origin of short-gamma ray burst, on the production site of of heavy elements in the Universe, and on cosmography. Future multimessenger…

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