Joint Israeli Seminar Series on Gravitational Physics

28/11: Robert Wald (Chicago)

Title: Black Holes Decohere Quantum Superpositions

Abstract: We show that if a massive body is put in a quantum superposition of spatially separated states, the mere presence of a black hole in the vicinity of the body will eventually destroy the coherence of the superposition. This occurs because, in effect, the gravitational field of the body radiates soft gravitons into the black hole, allowing the black hole to harvest "which path'' information about the superposition. A similar effect occurs for quantum superpositions of electrically charged bodies. The effect is very closely related to the memory effect and infrared divergences at null infinity.

12/12: Horng Sheng Chia (IAS)

Title: In Pursuit of Love: Black Holes and Gravitational Waves as Multifaceted Probes of the Universe

Abstract: Black holes and gravitational waves are remarkable probes of astrophysics and physics beyond the Standard Model. In this talk, I will start by briefly describing the tidal effects of black holes, including the vanishing Love numbers of Kerr black holes and the interesting dissipative phenomenon known as “superradiance.” I then discuss how black hole superradiance is a powerful probe of ultralight dark matter, as it allows for the spontaneous formation of bosonic bound states around highly-spinning black holes, also commonly known as the “gravitational atoms”. Finally, I will describe a recent search for new signals, specifically compact objects with large tidal Love numbers, in the public LIGO-Virgo data. While our work focuses on astrophysical bodies with large Love numbers in binary systems, this novel search strategy can be adapted to detect many new types of binaries that differ from the standard quasi-circular binary black holes.

16/1: Daniel Kapec (Harvard)

Title: The Kerr Black Hole as a Quantum System

Abstract:  To an outside observer, a black hole appears to be an ordinary quantum mechanical system with finite entropy and highly chaotic internal dynamics. Nevertheless, the low-temperature thermodynamics of the Kerr black hole presents several puzzles. For instance, the leading order semiclassical approximation to the black hole density of states predicts a surprisingly large ground state degeneracy, while poorly understood quantum corrections are known to become increasingly important at low temperatures. I will review the modern picture of black holes as quantum systems and then discuss a recent result on the leading correction to the low-temperature thermodynamics of the Kerr black hole that resolves many of the old puzzles.

30/1: Barak Kol (HUJI)

Title: The flux-based statistical theory of the three-body system

Abstract:  The three-body system in Newtonian gravity is one of the most fruitful and longest-standing open in physics. It was involved in the creation of several branches of science including physical perturbation theory, Poisson brackets, chaos and topology. 

This talk shall describe recent progress regarding the chaotic non-hierarchical case: a symmetric formulation of the problem and an exact reduction of its statistical solution. We shall focus on novel theoretical constructions. Strong evidence from computer simulations will be presented.

Based on: 

- BK, Natural dynamical reduction of the three-body problem, Celest. Mech. Dyn. Astron. 135, 29 (2023) [arXiv:2107.12372]

- BK, Flux-based prediction of three-body outcomes, Celest. Mech. Dyn. Astron. 133, 17 (2021) [arXiv:2002.11496]

- V. Manwadkar, A. Trani and BK, Measurement of three-body chaotic absorptivity predicts chaotic outcome distribution, accepted for publication by Celest. Mech. Dyn. Astron., arXiv:2302.08312

- And more.

13/2: Barak Zackay (Weizmann)

Title: The Current State of Ground-Based GW Astronomy and the Efforts to Study the Origin of Compact Objects in Relativistic Binaries

Abstract: In this talk, I will present the recent compact binary coalescence discoveries (using both the official LIGO pipelines, and ours) and present the current fronts in figuring out the origin of binary black holes (BBH).

I will then present the current efforts in my group to address the main questions: 

1) Is there a mass cutoff to stellar mass black holes? - This calls for searching the highest mass events using higher modes.

2) Do BBH form dynamically or through binary stellar evolution? - This motivates a search for precessing systems. 

3) Are Binary neutron star mergers always accompanied by a GRB? Is there a population of faint GRBs coming from BNS systems in which we are off the jet-axis? - This motivates us to improve GRB detection.

4) Does the spin magnitude of the black holes change with mass? This calls for better measurements of the found system's parameters. This is possible if we could remove noise from the low-freq part of the band, calling for the use of the auxiliary channels to cancel bi-linear noise sources.

27/2: Amos Yarom (Technion)

Title: Holographic turbulence

Abstract: I will discuss recent developments regarding the interplay between the dynamics of asymptotically anti de Sitter black branes and turbulent flow.

12/3: Ramy Brustein (BGU)

Title: Sourcing the Kerr geometry

Abstract: I will start by presenting general arguments as to why we should expect significant, horizon scale, departures from the classical Schwarzschild and Kerr geometries inside black holes. Then, I will present a simple model which realizes this idea: the Frozen Star model, briefly showing that a static frozen star looks exactly like a Schwarzschild black hole to an external observer and that it is sourced by a “string fluid”. The main part of the presentation is about the interior geometry of the rotating frozen star which modifies Kerr such that there is neither an inner ergosphere nor an inner horizon, and the metric and Einstein tensors are regular everywhere except for a mild, removable singularity at the center of the star. The geometry of each radial slice of the interior is a nearly null surface with the same geometry, but different radial size, as that of the would-be horizon on the outermost slice. The integral of the interior energy density of the “string fluid” source is equal to the irreducible mass of a Kerr black hole, and the integral of the angular-momentum density confirms that the ratio of the angular momentum to the mass is equal to the Kerr spin parameter. Including the rotational energy in the standard way, we then obtain the total gravitational mass and angular momentum of the corresponding Kerr black hole.

21/5: Alessandra Buonanno (AEI Postdam)

Title: TBA

Abstract: TBA