Strong Gravity research at Perimeter Institute is devoted to understanding both the theoretical and observational aspects of systems in which gravity is very strong (i.e., spacetime is highly curved or dynamical],. On one hand, this means studying extreme astrophysical systems, like black holes and neutron stars, as well as making and testing predictions for existing and forthcoming gravitational wave detectors, electromagnetic telescopes, and particle astrophysics experiments. On the other hand, it also includes a range of nonastrophysical topics, such as the instabilities of higherdimensional black holes or the dynamics of stronglycoupled quantum field theories (via holography). The goal of strong gravity researcher is to test the validity of Einstein's theory of gravity, constrain proposed alternatives, understand the most extreme astrophysical systems, and investigate the ways in which highly curved or dynamical spacetimes are linked with a range of other problems in fundamental physics.
Format results

34 talksCollection Number C17055
Talk

Quantifying the evidence for black holes with GW and EM probes
Paolo Pani Instituto Superior Tecnico  Departamento de Física

Echoes from the Abyss: Tentative Evidence for PlanckScale Structure at Black Hole Horizons
Jahed Abedi University of Stavanger (UiS)

Improvements on the methods for searching echoes
Julian Westerweck Albert Einstein Institute

A modelindependent search for gravitationalwave echoes
Archisman Ghosh Institucio Catalana de Recerca I Estudis Avancats (ICREA)  Universitat de Barcelona

An alternative significance estimation for the evidence for echoes
Alex Nielsen Albert Einstein Institute


Inspiral Tests of Strongfield Gravity and Ringdown Tests of Quantum Black Holes
Kent Yagi University of Virginia

A Recipe for Echoes
Aaron Zimmerman The University of Texas at Austin


Lights, Sounds, Action in Strong Field Gravity.
Collection Number C17062 
PSI 2017/2018  Relativity (Turok)
15 talksCollection Number C17036Talk

PSI 2017/2018  Relativity  Lecture 1
Neil Turok University of Edinburgh

PSI 2017/2018  Relativity  Lecture 2
Neil Turok University of Edinburgh

PSI 2017/2018  Relativity  Lecture 3
Neil Turok University of Edinburgh

PSI 2017/2018  Relativity  Lecture 4
Neil Turok University of Edinburgh

PSI 2017/2018  Relativity  Lecture 5
Neil Turok University of Edinburgh

PSI 2017/2018  Relativity  Lecture 6
Neil Turok University of Edinburgh

PSI 2017/2018  Relativity  Lecture 7
Neil Turok University of Edinburgh

PSI 2017/2018  Relativity  Lecture 8
Neil Turok University of Edinburgh


2016 Midwest Relativity Meeting
Collection Number C16047 
PSI 2016/2017  Relativity (Turok)
14 talksCollection Number C16010Talk

PSI 2016/2017  Relativity  Lecture 1
Neil Turok University of Edinburgh

PSI 2016/2017  Relativity  Lecture 2
Neil Turok University of Edinburgh

PSI 2016/2017  Relativity  Lecture 3
Neil Turok University of Edinburgh

PSI 2016/2017  Relativity  Lecture 4
Neil Turok University of Edinburgh

PSI 2016/2017  Relativity  Lecture 5
Neil Turok University of Edinburgh

PSI 2016/2017  Relativity  Lecture 6
Neil Turok University of Edinburgh

PSI 2016/2017  Relativity  Lecture 7
Neil Turok University of Edinburgh



EHT 2014
54 talksCollection Number C14041Talk

Welcome to Perimeter Institute and the EHT 2014 Conference
Neil Turok University of Edinburgh


Growth of supermassive black holes and their relationships to their host galaxies
Marta Volonteri Institut d'Astrophysique de Paris

Polarized emission from Black Hole Accretion Disks and Jets
Jonathan McKinney University of Maryland, College Park

Stellar Orbits at the Galactic Center
Andrea Ghez University of California, Los Angeles



Particle Acceleration and Nonthermal Emission in Radiatively Inefficient Accretion Flows
Eliot Quataert University of California System


Gyroscopes orbiting gargantuan black holes  VIRTUAL
Lisa Drummond Massachusetts Institute of Technology (MIT)

Gravitational attraction: dynamically enhanced formation of millisecond pulsars in globular clusters
Claire Ye Canadian Institute for Theoretical Astrophysics (CITA)

Quasinormal modes of a Schwarzschild white hole
Amos Kubeka University of South Africa

Multimessenger signals from electromagnetic decay of axion stars  VIRTUAL
Eugene Lim King's College London

Unveiling a Novel Plasma Instability: Impacts on Galaxy Formation and Electron Acceleration at Astrophysical Shocks
Mohamad Shalaby Leibniz Institute for Astrophysics Potsdam (AIP)

The quasinormalmode content of black hole ringdowns
Mark Cheung Johns Hopkins University

Quantum Black Holes in the Sky?
34 talksCollection Number C17055The past decade has witnessed significant breakthroughs in understanding the quantum nature of black holes, with insights coming from quantum information theory, numerical relativity, and string theory. At the same time, astrophysical and gravitational wave observations can now provide an unprecedented window into the phenomenology of black hole horizons. This workshop seeks to bring together leading experts in these fields to explore new theoretical and observational opportunities and synergies that could improve our physical understanding of quantum black holes.

Lights, Sounds, Action in Strong Field Gravity.
Collection Number C17062With LIGO/VIRGO in operation and detecting gravitational waves, the era of gravitational wave astronomy is upon us. In anticipation of further observations, this workshop will discuss the physics, astrophysics, and observational prospectsas well as challengesin gravitational wave sources including black holes, neutron stars, and other fascinating objects, in both the near and long term.

PSI 2017/2018  Relativity (Turok)
15 talksCollection Number C17036PSI 2017/2018  Relativity (Turok) 

PSI 2016/2017  Relativity (Turok)
14 talksCollection Number C16010PSI 2016/2017  Relativity (Turok) 

Gyroscopes orbiting gargantuan black holes  VIRTUAL
Lisa Drummond Massachusetts Institute of Technology (MIT)
Extreme massratio binary black hole systems, known as EMRIs, are expected to radiate lowfrequency gravitational waves detectable by planned spacebased Laser Interferometer Space Antenna (LISA). We hope to use these systems to probe black hole spacetimes in exquisite detail and make precision measurements of supermassive black hole properties. Accurate models using general relativistic perturbation theory will allow us to unlock the potential of these unique systems. Such models must include postgeodesic corrections, which account for forces driving the smaller black hole away from a geodesic trajectory. When a spinning body orbits a black hole, its spin couples to the curvature of the background spacetime, introducing postgeodesic correction called the spincurvature force. In this talk, I will present our calculation of EMRI waveforms that include both spincurvature forces and the leading backreaction due to gravitational radiation. We use a nearidentity transformation to eliminate dependence on the orbital phases, allowing for very fast computation of completely generic worldlines of spinning bodies; such efficiency is crucial for LISA data analysis. Finally, I will discuss what aspects still need to be included in future calculations so that we can use EMRIs for a new era of precision gravitationalwave astronomy, addressing outstanding puzzles in astrophysics, cosmology and fundamental theoretical physics.

Zoom link https://pitp.zoom.us/j/91917788358?pwd=MWp5OUhxbkRmZDFxWWE4cHR0VlBTUT09

Gravitational attraction: dynamically enhanced formation of millisecond pulsars in globular clusters
Claire Ye Canadian Institute for Theoretical Astrophysics (CITA)
A high specific abundance of millisecond radio pulsars has been observed in globular clusters (GCs), motivating theoretical studies of the formation and evolution of these sources through stellar evolution coupled to stellar dynamics. In this talk, I will first demonstrate how we model millisecond pulsars in GCs using realistic cluster simulations. I will show the importance of electroncapture supernovae for neutron star retention, and how millisecond pulsar formation is greatly enhanced through dynamical interaction processes. I will also present some latest results on isolated millisecond pulsars, which are especially intriguing given the fact that millisecond pulsars are descendants of binary star systems. I will demonstrate the potential formation channels of isolated millisecond pulsars, some of which may also link to the formation of magnetars and the newly discovered fast radio bursts in a GC.

Zoom link https://pitp.zoom.us/j/97622593487?pwd=SHNoM1o3T1JjWVROTkJoZ0NWYmdyQT09

Quasinormal modes of a Schwarzschild white hole
Amos Kubeka University of South Africa
We investigate perturbations of the Schwarzschild geometry using a linearization of the Einstein vacuum equations within a BondiSachs, or null cone, formalism. We develop a numerical method to calculate the quasinormal modes, and present results for the case ℓ= 2. The values obtained are different than those of a Schwarzschild black hole, and we interpret them as quasinormal modes of a Schwarzschild white hole.

Zoom link https://pitp.zoom.us/j/93648313308?pwd=akZMZXFKejIwdFphOVU0ZjFpeW13dz09

Multimessenger signals from electromagnetic decay of axion stars  VIRTUAL
Eugene Lim King's College London
If axion Dark Matter exists, then they can collapse to form selfgravitating exotic compact objects known as axion stars. As mergers of such compact objects can potentially yield detectable gravititational waves which are correlated with a burst of electromagnetic radiation, much effort have been expended to compute these signals. I will discuss both the technical and theoretical challenges of this endeavour, and demonstrate such decays. I will show that axion stars may not be stable to electromagnetic decay, raising the question on whether we should expect to see these objects in the first place.

Zoom link https://pitp.zoom.us/j/98298572209?pwd=WVFZUFJqQzZQdU8vcjhQRVpzVHZDdz09

Unveiling a Novel Plasma Instability: Impacts on Galaxy Formation and Electron Acceleration at Astrophysical Shocks
Mohamad Shalaby Leibniz Institute for Astrophysics Potsdam (AIP)
Cosmicraydriven instabilities play a crucial role in particle acceleration at shocks and during the propagation of GeV cosmic rays in galaxies and galaxy clusters within the selfconfinement picture of CR transport. These instabilities amplify magnetic fields, which, in turn, scatter cosmic rays and thus selfregulate their transport. This leads to a strong coupling between the collisionless cosmic ray population and the thermal background plasma, implying potentially significant dynamic feedback. In this presentation, I discuss a recent discovery of a new cosmic raydriven instability, referred to as the intermediatescale instability, which triggers comoving ioncyclotron electromagnetic waves at subion skindepth scales. Its growth rate is notably faster compared to the ion gyro scale (streaming) instability, which is commonly assumed to be the dominant instability in the selfconfinement picture. Therefore, this new instability could play a vital role in the transport of cosmic rays in galactic and stellar environments. I then explore the implications of this instability for electron acceleration at nonrelativistic shocks. Through Particleincell (PIC) simulations, it is demonstrated that the new instability triggers the dominant mechanism for efficient electron acceleration at parallel electronion shocks, addressing a persistent issue with electron injection at these shocks. The PIC simulations also reveal that the common practice of using reduced iontoelectron mass ratios in shock simulations, which artificially suppresses the intermediate instability, not only hinders electron acceleration but also leads to incorrect electron and ion heating in downstream and shock transition areas.

Zoom link https://pitp.zoom.us/j/91367222746?pwd=REpEdXE3ZGdLeVQ1bnh0NldIQktWQT09

The quasinormalmode content of black hole ringdowns
Mark Cheung Johns Hopkins University
In general relativity, the remnant black hole of a binary black hole merger emits “ringdown” radiation: a superposition of quasinormal modes with characteristic complex frequencies. The detection of more than one of these frequencies would serve as smokinggun evidence of a black hole and would enable a test of the nohair theorem. In this talk, I will discuss strategies for identifying quasinormal modes within simulated ringdown waveforms both in linear perturbation theory and full general relativity. I will show that a rich spectrum of modes could exist in the ringdown, including overtones, retrograde modes and nonlinear modes, and that interesting quasiuniversal relationships exist between some of their amplitudes. I will also discuss the spectral instability of quasinormal modes and its potential imprints on the ringdown waveform. These results could guide the analysis of real ringdown signals detected by gravitationalwave detectors.

Zoom link https://pitp.zoom.us/j/92002625163?pwd=bHNDVVZKYnVNTENLNXJBLzVNKzVSQT09