GR Amaldi Papers

Wednesday 23 Jul 2025, 12:30 → 14:00 Europe/Rome

There will be presented the following papers listed below.

Title: "GW231123: a Binary Black Hole Merger with Total Mass 190-265 ⊙"

 

Abstract:

On 2023 November 23 the two LIGO observatories both detected GW231123, a gravitational-wave signal consistent with the merger of two black holes with masses 137+22 −17 M⊙ and 103+20 −52 M⊙ (90% credible intervals), at luminosity distance 0.7–4.1 Gpc and redshift of 0.39+0.27 −0.24, and a network signal to-noise ratio of ∼22.5. Both black holes exhibit high spins, 0.90+0.10 −0.19 and 0.80+0.20 −0.51 respectively. A massive black hole remnant is supported by an independent ringdown analysis. Some properties of GW231123 are subject to large systematic uncertainties, as indicated by differences in inferred parameters between signal models. The primary black hole lies within or above the theorized mass gap where black holes between 60–130 M⊙ should be rare due to pair instability mechanisms, while the secondary spans the gap. The observation of GW231123 therefore suggests the formation of black holes from channels beyond standard stellar collapse, and that intermediate-mass black holes of mass ∼200 M⊙ form through gravitational-wave driven mergers.

Arxiv link: https://arxiv.org/pdf/2507.08219

Title: "Unstable chords and destructive resonant excitation of black hole quasinormal modes"

 

Abstract:

The quasinormal mode spectrum of black holes is unstable against small modifications of the radial potential describing massless perturbations. We study how these small modifications affect the convergence of the quasinormal mode expansion and the mode excitation by computing the mode amplitudes from first principles, without relying on any fitting procedure. We show that the decomposition of the prompt ringdown waveform is not unique: small modifications in the radial potential produce new quasinormal mode “basis sets” that can improve the convergence of the quasinormal mode expansion, even capturing the late-time tail. We also study avoided crossings and exceptional points of the Kerr and Kerr-de Sitter spectrum. We show that while the mode amplitude can be resonantly excited, modes that exhibit avoided crossing destructively interfere with each other, so that the prompt ringdown waveform remains stable.

Arxiv link: https://arxiv.org/pdf/2503.21276