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.

Dynamic and Thermodynamic Stability of Black Holes and Black Branes

Thursday Jun 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, an

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Spinning black-hole binaries as gravitational and cosmological probes

Friday Jun 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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Initial-boundary value problems for Einstein's field equations

Thursday May 23, 2013
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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

Thursday May 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

Thursday May 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
as almost-model-independent smoking guns for exotic particles and modified gravity, as well as their limitations in realistic astrophysical scenarios, are discussed.

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Constraining neutron star interior properties with transient events from accreting neutron stars and magnetars

Thursday Apr 25, 2013
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The last few years have seen new opportunities for
constraining the physics of neutron star interiors. I will first discuss the
current state of neutron star radius measurements and then go on to discuss
thermal tomography as a probe of the nuclear, magnetic, and transport
properties of neutron star crusts. In each case, I will emphasize the
astrophysics that must be understood to make reliable inferences about the
properties of dense matter from observations of neutron stars.

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Spinning black-hole binaries as gravitational and cosmological probes

Thursday Apr 11, 2013
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Fundamental Physics with Optically Levitated Dielectric Objects

Thursday Apr 04, 2013
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In the past few years, optical
cooling and manipulating of macroscopic objects, such as micro-mirrors and
cantilevers has developed into an active field of research.
In mechanical systems, the oscillator is attached to its suspension,
a thermal contact that limits the motion isolation. On the other hand, when
these small objects are levitated using the radiation pressure force of lasers,
the excellent thermal isolation even at room temperatures helps produce
very sensitive force detectors, and eventually quantum transducers for quantum

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Shake, Rattle and Explode: Short GRBs and the Electromagnetic Counterparts of Gravitational Wave Sources

Tuesday Apr 02, 2013
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The bimodality of gamma-ray burst (GRB) durations points
to distinct progenitor classes for the long- and short-duration GRBs. While the
progenitors of long-duration GRBs are now known to be massive stars, the
progenitors of short-duration GRBs remain unidentified. In this talk I will
discuss the discovery of short GRB afterglow and their host galaxies, detailed
studies of their environments from parsec to galactic scales, and studies of
their energetics and beaming. Taken together, these observations point to the

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Particle Acceleration by Magnetic Reconnection in Striped Pulsar Winds and Relativistic Jets

Thursday Mar 21, 2013
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The relativistic wind of pulsars consists of toroidal
stripes of opposite magnetic field polarity, separated by current sheets of hot
plasma. By means of 2D and 3D particle-in-cell simulations, we investigate
particle acceleration and magnetic field dissipation at the termination shock
of a striped pulsar wind. At the shock, the flow compresses and the alternating
fields annihilate by driven magnetic reconnection. Irrespective of the stripe
wavelength "lambda" or the wind magnetization "sigma" (in

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