Fall semester 2025/26
9/12: Frans Pretorius (Princeton) (special time: 17:00)
Title: Open Questions on the Dynamics of Black Holes
Abstract: Today we have a solid theoretical understanding of the dynamics of black
holes, as predicted by general relativity, for the typical binary merger
expected as an astrophysical gravitational wave source.
However, in more "extreme" situations, namely black holes that collide with
ultrarelativistic velocities, and black holes that spin near the maximal limit
allowed by general relativity, less is known, in some cases even qualitatively.
In this talk I will discuss some of these open questions,
and speculate about possible answers.
20/1: Achilleas Porfyriadis (University of Crete)
Title: Approaching a dynamical extreme black hole horizon
Abstract: There exist dynamical extreme Reissner-Nordstrom (DERN) black holes. These are spherically symmetric dynamical solutions of Einstein-Maxwell theory coupled to a neutral scalar that feature: (i) a spacetime metric which tends to that of a static extreme Reissner-Nordstrom (RN), and (ii) a scalar field which exhibits the linear Aretakis instability ad infinitum in the non-linear theory. We employ the two-dimensional Jackiw-Teitelboim (JT) gravity to give an explicit closed form description of the late-time near-horizon approach to DERN.
27/1: Adam Pound (Southampton)
Title: Modeling asymmetric binaries: inspiral, merger, and ringdown in gravitational self-force theory
Abstract: High-mass-ratio binaries, such as extreme-mass-ratio inspirals in galactic cores, will be important sources for future gravitational-wave detectors. The premier method of modeling these binaries is gravitational self-force theory, which has enabled fast, first-principles waveform models and achieved surprisingly high accuracy even for comparable-mass systems. In this talk, I summarize the state of the art in the field, particularly recent work that has extended the method into the merger-ringdown regime. I highlight how these self-force calculations can provide fast inspiral-merger-ringdown models as well as new insights into the merger and ringdown process.
3/2: Alessandro Podo (IHES)
Title: Naturalness of vanishing black-hole tides
Abstract: I will present a symmetry argument for the vanishing and non-renormalization of static Love numbers for spherically symmetric black holes at nonlinear order, in D=4 classical General Relativity. The symmetry is realized both in full GR and in the worldline EFT, allowing for a unified treatment. This clarifies the naturalness of vanishing static Love numbers in the worldline EFT when including non-linearities, and extends previous vanishing results to all nonlinear static tides. When extended to higher dimensional gravity, this also explains the pattern of vanishing and running static Love numbers of electric and tensor type, and predicts new results at the nonlinear order. I will also apply the same arguments to the tidal response of shift-symmetric scalar fields, predicting new zeros and unifying them with the no-hair theorem for shift-symmetric scalar fields (and its violations). If time permits, I will also comment on the extension of these results to backgrounds with electro-magnetic and gravito-magnetic charges. Based on joint work with Julio Parra-Martinez.
Spring semester 2025/26
12/3: Mykhaylo Usatyuk (KITP)
Title: Near-extremal black hole evaporation
Abstract: Over the last few years it has been understood that black holes sufficiently close to extremality receive large quantum corrections that modify their thermodynamic properties. In this talk, I will explain how these large corrections modify the real time dynamics of near-extremal black holes. As an example, the spectrum of emitted Hawking radiation differs drastically from the standard predictions of QFT in curved spacetime for such black holes.
16/4: Ofek Birnholtz (BIU)
Title: The Gravitational Wave Transient Catalog 4.0: Overview and Highlights
Abstract: The worldwide network of gravitational-wave (GW) detectors, comprised of the Advanced LIGO, Advanced Virgo, and KAGRA detectors has been increasing in sensitivity, range, and hence quantity and quality of detected GW signals from compact binary coalescences. We present the compact binary signals observed and included in the GW Transient Catalog 4 (GWTC-4), i.e. up to and including the first part of the fourth observing run of the detectors (O4a). We estimate the source properties, and provide new insight into compact objects in binaries - and to what may lay ahead.
30/4: Emanuele Berti (Johns Hopkins)
Title: Nonlinearities, greybody factors and resonances in black hole ringdown
Abstract: According to general relativity, the remnant of a binary black hole merger is a perturbed Kerr black hole. Perturbed Kerr black holes emit "ringdown" radiation which is well described by a superposition of damped exponentials ("quasinormal modes”), with frequencies and damping times that depend only on the mass and spin of the remnant. The observation of gravitational radiation emitted by black hole mergers might finally provide direct evidence of black holes, just like the 21 cm line identifies interstellar hydrogen. I will discuss some recent developments in the "black hole spectroscopy" program. I will focus on the modeling of nonlinearities in the ringdown, greybody factor models of the frequency-domain waveform, avoided crossings of quasinormal modes, and the possibility of resonant mode excitation.
25/6: Dina Meylakh (HUJI)
Title: Tidal Response and Thermodynamics of Black Holes
Abstract: In this work, we revisit black hole Love numbers from two complementary perspectives. First, we develop a manifestly gauge-invariant framework that directly integrates out the short-distance degrees of freedom of a static black hole in arbitrary spacetime dimensions. This approach yields the effective point-particle action and its associated Love numbers without relying on the standard matching procedure or on the Regge-Wheeler equation and its associated master field. Second, we investigate the role of Love numbers in black hole thermodynamics by analyzing a Schwarzschild black hole subjected to various types of external perturbations. We show that Love numbers govern the induced polarization of the black hole and control the leading corrections to its thermodynamic properties, thereby clarifying their physical significance in black hole thermodynamics.