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.
 

 

Thursday Nov 26, 2020
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Abstract: Gamma-ray bursts (GRBs) associated with gravitational wave events are, and will likely continue to be, viewed at a much larger inclination than GRBs without gravitational wave detections.  Viewing GRBs and their afterglows at large inclination can massively affect the observed electromagnetic emission, as dramatically demonstrated by the binary neutron star merger event GW170817.  Analyzing this event and future ones requires an extension of the common GRB afterglow models which typically assume emission from a structureless (top-hat) jet viewed on-axis.

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Thursday Nov 19, 2020
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Compact binaries may be formed dynamically in globular clusters, with large (close to unity) orbital eccentricity and emitting gravitational waves within the detection band of ground based detectors. The gravitational waves from such sources resemble more a discrete set of bursts than the continuous signal of their quasi-circular counterparts. I here discuss the construction of new analytic waveforms for such systems, which rely on treating the problem as a perturbation of a parabolic fly-by.

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Thursday Nov 12, 2020

We have tentative evidence of massive stars that disappear without a bright transient. It is commonly argued that this massive stars have low angular momentum and can collapse into a black hole without significant feedback. In this talk I will make use of general-relativistic hydrodynamical simulations to understand the flow around a newly-formed black hole. I will discuss the angular momentum needed in order for the infalling material to be accreted into the black hole without forming a centrifugally supported structure, thus generating no effective feedback.

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Thursday Nov 05, 2020

Abstract and Zoom Link: TBD

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Thursday Oct 29, 2020
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Millisecond Pulsars (MSPs) have become reliable and
extremely stable workhorses of modern astronomy and physics.  The
North American Nanohertz Observatory for Gravitational Waves, or
NANOGrav, has been observing growing numbers of these systems for over
15 years, and the data look great.  High precision timing of almost 80
MSPs has provided unprecedented sensitivity to the gravitational wave
Universe at nHz-frequencies, where our upper limits are already
constraining the population of super-massive black hole binaries.  But

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Thursday Oct 22, 2020
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Extreme-mass-ratio inspirals (EMRIs) are the only gravitational-wave sources for the future LISA detector that combine the issue of strong-field complexity with that of long-lived signals. The result is a profoundly difficult inverse problem, with many theoretical and computational challenges presented both by the forward modeling of the predicted EMRI waveform, and by the recovery of an inverse solution for the presence and properties of actual EMRI signals in LISA data. I outline recent progress and ongoing work on both fronts.

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Thursday Oct 08, 2020
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The astrophysical background of gravitational waves (AGWB) is composed by the incoherent superposition of gravitational wave signals emitted by resolved and unresolved astrophysical sources from the onset of stellar activity until today. In this talk, I  will present a theoretical framework  to characterize the AGWB in terms of energy density and polarization and  I will show predictions for the angular power spectra of the background anisotropy and for its cross-correlations with electromagnetic observables, in the frequency bands accessible by  LIGO/Virgo and  LISA.  I will then discuss t

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Thursday Oct 01, 2020
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Gravitational waves from the coalescence of compact binaries provide a unique opportunity to test gravity in strong field regime. In particular, the postmerger phase of the gravitational signal is a proxy for the nature of the remnant.

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Thursday Sep 24, 2020
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The statement that general relativity is deterministic finds its mathematical formulation in the celebrated ‘Strong Cosmic Censorship Conjecture’ due to Roger Penrose. I will present my recent results on this conjecture in the case of negative cosmological constant and in the context of black holes. It turns out that this is intimately tied to Diophantine properties of a suitable ratio of mass and angular momentum of the black hole.

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Thursday Sep 17, 2020

Quasars are the most luminous objects in the universe powered by accretion onto supermassive black holes (SMBHs). They can be observed at the earliest cosmic epochs, providing unique insights into the early phases of black hole, structure, and galaxy formation. Observations of these quasars demonstrate that they host SMBHs at their center, already less than ~1 Gyr after the Big Bang.

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