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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.

## 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.

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## New lessons about hydrodynamics from gravity

Jeudi oct 31, 2013
Speaker(s):

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
Speaker(s):

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

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## Plasma without Plasma: Exploring Force-Free Magnetospheres

Jeudi oct 10, 2013
Speaker(s):

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
Speaker(s):

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,

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## Spinning black-hole binaries as gravitational and cosmological probes

Vendredi juin 07, 2013
Speaker(s):

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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## Initial-boundary value problems for Einstein's field equations

Jeudi mai 23, 2013
Speaker(s):

We discuss well-posed initial-boundary value formulations
in general relativity. These formulations allow us to construct solutions of
Einstein's field equations inside a cylindrical region, given suitable initial
and boundary data. We analyze the restrictions on the boundary data that result
from the requirement of constraint propagation and the minimization of spurious
reflections, and choosing harmonic coordinates we show how to cast the problem
into well-posed form. Then, we consider the particular case where the boundary

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## Detectable signatures of compact binaries involving neutron stars

Jeudi mai 16, 2013
In this talk I will focus on two topics concerning compact binaries that involve a neutron star companion: a) the fate of and observable signatures from merging white dwarf-neutron star (WDNS) binaries, and b) electromagnetic signals from black hole - neutron star (BHNS) binaries.
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## David Defeats Goliath: How Ultralight Fields Affect The Dynamics of Massive Black Holes

Jeudi mai 09, 2013
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In the last few years several interesting phenomena associated to the interaction between massive black holes and fundamental bosonic fields have been discovered. I present a selection of them, including superradiance instabilities of spin-0, spin-1 and spin-2 fields, floating orbits in extreme-mass ratio inspirals and black-hole spontaneous scalarization. The theoretical potential of these effects

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## RECENT PUBLIC LECTURE

### Mario Livio: Brilliant Blunders

Speaker: Mario Livio