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
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Thursday Feb 09, 2017Speaker(s):
We will discuss how the process of superradiance, combined with
gravitational wave measurements, makes black holes into
nature's laboratories to search for new light bosons. We will present
analytic results for superradiance of light vector (spin-1) particles,
valid in the regime where the vector's Compton wavelength is much
larger than the horizon size of a black hole. If superradiance is
efficient, the occupation number of the vectors in the black hole's
vicinity grows exponentially and the black hole spins down. We willCollection/Series:Scientific Areas:
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Thursday Jan 26, 2017Speaker(s):
The modeling of pulsar radio and gamma-ray emission suggests that in order to interpret the observations one needs to understand the field geometry and the plasma state in the emission region. In recent years, significant progress has been achieved in understanding the magnetospheric structure in the limit of abundant plasma supply. However, the very presence of dense plasma everywhere in the magnetosphere is not obvious. Even the region where the observed emission is produced is subject to debate.
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Thursday Jan 19, 2017Speaker(s):
The first detections of gravitational waves by LIGO-Virgo initiated the era of Gravitation-Wave Astronomy. Gravitational-waves serve as a new and independent probe of the Universe. In addition, the combination of gravitational-waves with information from other messengers, such as electromagnetic emission from the same source, will lead to a more complete and accurate understanding of cosmology and astrophysics. In this talk, I will discuss some interesting learnings from the Advanced LIGO-Virgo first observing run and several scientific goals we expect to reach in the next few years.
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Thursday Nov 24, 2016Speaker(s):
The anti-de Sitter (AdS) space is of great interest in contemporary
theoretical physics due to the AdS/CFT correspondence. However, the
question of stability of AdS space is unanswered till now. After
giving the motivation for studies of asymptotically AdS spaces, I will
review dynamics of such spacetimes in the context of AdS instability
problem. This survey will include: evidence for instability of AdS
space, existence and properties of time-periodic solutions, andCollection/Series:Scientific Areas:
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Thursday Nov 17, 2016Speaker(s):
Massive objects orbiting a near-extreme Kerr black hole plunge into the horizon after passing the innermost stable circular orbit, producing a potentially observable signal of gravitational radiation. The near horizon dynamics of such rapidly rotating black holes is governed by a conformal symmetry. In the talk I will show how this symmetry can be exploited to analytically compute the gravitational waves produced by a variety of orbits. I will also discuss an application to gravitational self-force and comment on the holographic interpretation of the process.
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Thursday Nov 03, 2016Speaker(s):
Galaxy mergers are a standard aspect of galaxy formation and evolution, and most (likely all) large galaxies contain supermassive black holes. As part of the merging process, the supermassive black holes should in-spiral together and eventually merge, generating a background of gravitational radiation in the nanohertz to microhertz regime. Processes in the early Universe such as relic gravitational waves and cosmic strings may also generate gravitational radiation in the same frequency band.
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Thursday Oct 20, 2016Speaker(s):
On September 14th and December 26th, 2015, the Advanced LIGO detectors observed two gravitational wave signals, each from the merger of stellar-mass black holes. These two observations have given us the first glimpse in to the population of stellar mass black holes. In this talk I will discuss these first detections of gravitational waves including the non-detection of gravitational waves from the merger of binary neutron star and neutron star black holes systems.
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Thursday Sep 15, 2016Speaker(s):
LIGO's first observing run which ended in January 2016 yielded two unambiguous gravitational wave signals (GW150914 and GW151226) from the merger of binary black holes as well as a possible third signal (LVT151012). I will review our current estimates of the parameters of the source systems as well as possible formation scenarios. I will discuss how joint analyses of GW150914 and GW151226 allow us to place bounds on departures from general relativity, infer astrophysical binary black hole formation rates, and constrain the mass distribution of coalescing black hole systems.
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Thursday Sep 01, 2016Speaker(s):
We reconsider a gauge theory of gravity in which the gauge group is the conformal group SO(4,2), and the action is of the Yang-Mills form, quadratic in the curvature. The vacuum sector of the resulting gravitational theory exhibits local conformal symmetry. We allow for conventional matter coupled to the spacetime metric as well as matter coupled to the field that gauges special conformal transformations. When the theory is linearized about flat space, we find there is a long range gravitational force in addition to Newton’s inverse square law.
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Thursday Aug 18, 2016Speaker(s):
Aretakis' discovery of a horizon instability of extremal black holes came as something of a surprise given earlier proofs that individual frequency modes are bounded. Is this kind of instability invisible to frequency-domain analysis? The answer is no: We show that the horizon instability can be recovered in a mode analysis as a branch point at the horizon frequency. We use the approach to generalize to nonaxisymmetric gravitational perturbations and reveal that certain Weyl scalars are unbounded in time on the horizon.
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