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Strong Gravity

This series consists of talks in areas where gravity is the main driver behind interesting or peculiar phenomena, from astrophysics to gravity in higher dimensions.

Seminar Series Events/Videos

Currently there are no upcoming talks in this series.

Collisions in AdS and the thermalisation of heavy-ion collisions

Jeudi nov 28, 2013
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The motivation of this seminar is to understand the thermalisation of heavy ion collisions using AdS/CFT. These collisions can be modelled as colliding planar gravitational shock waves. This gives rise to rich and interesting dynamics; wide shocks come to a full stop and expand hydrodynamically, as was previously found by Chesler and Yaffe. High energy collisions (corresponding to thin shocks) pass through each other, after which a plasma forms in the middle, within a proper time 1/T, with T the local temperature at that time.

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Charged particle motion in magnetized black holes

Jeudi nov 21, 2013
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There exist evidences that magnetic field in
the vicinity of astrophysical black holes plays an important role. In
particular it is required for explanation of such phenomenon as jet formation.
Study of such problems in all their complexity requires 3D numerical
simulations of the magnetohydrodynamics in a strong gravitational field. Quite
often when dealing with such a complicated problem it is instructive to
consider first its simplifications, which can be treated either analytically,

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Self-force and Green function in Schwarzschild spacetime via quasinormal modes and branch cut

Jeudi nov 14, 2013
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The modelling of gravitational wave sources is of timely interest given the exciting prospect of a first detection of gravitational waves by the new generation of detectors. The motion of a small compact object around a massive black hole deviates from a geodesic due to the action of its own field, giving rise to a self-force and the emission of gravitational waves. The self-force program has recently achieved important results using well-established methods.

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Dynamical Emergence of Universal Horizons during the formation of Black Holes

Jeudi nov 07, 2013
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In many theories with fundamental preferred frame, such as Einstein-Aether or Gravitational Aether theories, K-essence, Cuscuton theory, Shape Dynamics, or (non-projectable) Horava-Lifshitz gravity, the low energy theory contains a fluid with superluminal or incompressible excitations. In this talk, I study the formation of black holes in the presence of such a fluid. In particular, I focus on the incompressible limit of the fluid (or Constant Mean Curvature foliation) in the space-time of a spherically collapsing shell within an asymptotically cosmological space-time.

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New lessons about hydrodynamics from gravity

Jeudi oct 31, 2013
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Hydrodynamics of relativistic plasmas received,
within the last 10 years, a lot of attention. The reason for it, on one hand,
is the quest for theoretical understanding of the quark-gluon plasma created in
heavy ion collisions and, on the other, advances in holographic duality and
black hole physics in anti-de Sitter spacetimes. I will describe recent
progress in answering foundational issues in hydrodynamics of strongly coupled
systems, i.e. questions about its applicability and the character of

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Quasinormal modes of rapidly rotating black holes/ Stability of tidally perturbed neutron stars

Jeudi oct 17, 2013
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I
will review recent work in two very different topics. First, I will discuss the
quasinormal mode spectrum of nearly extremal Kerr black holes, where a
bifurcation of the frequency spectrum is observed. In addition, collective
oscillations of many modes is possible, resulting in a power-law rather than
exponentially decaying ringdown. Next, I will discuss a recent proposal for how
tidally induced, multimode coupling of normal modes in neutron stars can
destabilize the stars. Such an instability could hamper gravitational wave

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Plasma without Plasma: Exploring Force-Free Magnetospheres

Jeudi oct 10, 2013
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Pulsars have enormous magnetic fields whose energy density
dwarfs the rest mass density of their plasma magnetosphere. In this
regime of a plasma, the particles drop out of the description, leaving a set of
equations for the electromagnetic field alone. This non-linear,
deterministic system is known as force-free electrodynamics, and turns out to
have some beautiful and bizarre features. I will give a pedagogical
introduction to these equations and their role in astrophysics and then discuss

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Neutron Stars and the Dense Matter Equation of State

Jeudi aoû 08, 2013
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Implications of
recently well-measured neutron star masses, particularly near and above 2 solar masses, for the equation of state (EOS) of neutron star matter will be highlighted.  Model independent upper

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Dynamic and Thermodynamic Stability of Black Holes and Black Branes

Jeudi juin 13, 2013
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I describe recent work with with Stefan Hollands that establishes a new criterion for the dynamical stability of black holes in $D \geq 4$ spacetime dimensions in general relativity with respect to axisymmetric perturbations: Dynamic stability is equivalent to the positivity of the canonical energy, $\mathcal E$, on a subspace of linearized solutions that have vanishing linearized ADM mass, momentum, and angular momentum at infinity and satisfy certain gauge conditions at the horizon.  We further show that $\mathcal E$ is related to the second order variations of mass, angular momentum, and

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Spinning black-hole binaries as gravitational and cosmological probes

Vendredi juin 07, 2013
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Spins play a major role in the strong-field dynamics of
black-hole binaries and their gravitational-wave emission. By detecting spin
effects in the waveforms, existing and future gravitational-wave detectors
therefore provide a natural way to test gravity in strong-field, highly
dynamical regimes.

In the first part of my talk, I will show that the
inclusion of the spins in the gravitational templates for future space-based
detectors will permit testing scenarios for the formation and cosmological

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LECTURES ON-DEMAND

Avery Broderick: Perimeter Institute and University of Waterloo

Speaker: Avery Broderick