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.

# Events Archive

## Gravity Initiative Seminar

### PGI Fall Seminar Series| Sam Gralla| University of Arizona|"Surprises in Gravitational Scattering"

### PGI Fall Seminar Series| Aaron Held| Princeton University|"Black Holes Beyond General Relativity: Shadows, Stability, and Nonlinear Evolution"

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.

### PGI Fall Seminar Series|Hsin-Yu Chen-Einstein Fellow, MIT|"Gravitational-wave Multimessenger Observations from the Production of Gold to the Expansion of the Universe"

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.

### PGI Fall Seminar Series| Stefan Czimek| Brown University|"The Characteristic Gluing Problem of General Relativity"

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.

### PGI Fall Seminar Series| Georgios Moschidis| Princeton University|"The Instability of Anti-de Sitter Spacetime for the Einstein-scalar Field System"

### PGI Fall Seminar Series| Keefe Mitman|Caltech| "Gravitational Waves in Numerical Relativity and the Importance of BMS Frames"

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### PGI Fall Seminar Series|Alejandro Cárdenas-Avendaño|Princeton University|"Quantifying the Unknown Using Electromagnetic and Gravitational Observations of Compact Objects"

Abstract: Over the past years, electromagnetic and gravitational observations have been used to understand the nature of compact objects and the matter around them.

### PGI Virtual Seminar Series | Elisa Maggio, University of Rome "Testing the nature of dark compact objects with gravitational waves"

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.

### PGI Virtual Seminar Series | Claude Warnick, Cambridge University "Quasinormal modes of black holes"

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.

### PGI Virtual Seminar Series | Marcelo Disconzi, Vanderbilt University "General-relativistic viscous fluids

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.

### PGI Virtual Seminar Series | Lydia Bieri, University of Michigan "New Structures in Gravitational Radiation"

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.

### PGI Virtual Seminar Series | Chris White, PU "Misaligned Accretion Flows and Their Impact on Black Hole Observations"

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.

### PGI Virtual Seminar Series | Brianna Grado-White, Brandeis "Multi-mouth Traversable Wormholes"

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### PGI Virtual Seminar Series | Eliot Quataert, PU "Horizon-scale Modeling of Black Hole Accretion"

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.

### PGI Virtual Seminar Series | Maya Fishbach, NU "Minding the Gap: Lessons from LIGO-Virgo’s Biggest Black Holes"

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### PGI Virtual Seminar Series | Antony Speranza, PI "Symmetries, observables, and entropy of black hole horizons"

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### PGI Virtual Seminar Series | Grigorios Fournodavlos, Sorbonne Université "Stable Big Bang formation"

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...

### Virtual Seminar Series | Sebastiano Bernuzzi (Friedrich-Schiller-Universität Jena) "Modeling the strong-field dynamics of binary neutron star merger"

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.

### PGI Virtual Seminar Series | Fani Dosopoulou, "The Merger History of Elliptical Galaxies: Mass Deficit"

Abstract: The structure and kinematics of galactic nuclei are fossil relics of the merger histories of galaxies and of the interaction between stars and SMBH binaries. Stars ejection during the SMBH binary evolution should reduce a galaxy’s central density and expand its core.

### PGI Virtual Seminar Series | Eliot Hijano Cubelos, "Where are BMS symmetries in the flat limit of AdS/CFT?"

Abstract: A holographic description of physics in Minkowski space is still elusive. A tempting approach is to implement a flat limit from AdS/CFT. Such a limit has not properly been understood, even at the level of the symmetries of the theory; How do BMS symmetries emerge from the flat limit of the asymptotic symmetries of anti-de Sitter space...