Considerations on the excitation of black hole quasinormal modes

TL;DR

This paper discusses the likelihood and mechanisms of exciting black hole quasinormal modes in various astrophysical scenarios, highlighting the challenges and gaps in current understanding for gravitational wave modeling.

Contribution

It provides a critical analysis of QNM excitation mechanisms, emphasizing the unlikelihood of resonant excitation by hyperaccretion and identifying key areas needing further research.

Findings

Resonant QNM excitation by hyperaccretion is highly unlikely due to fine-tuning requirements.

Current estimates of QNM excitation from collapse and collisions are summarized.

The paper identifies urgent research needs in gravitational wave source modeling.

Abstract

We provide some considerations on the excitation of black hole quasinormal modes (QNMs) in different physical scenarios. Considering a simple model in which a stream of particles accretes onto a black hole, we show that resonant QNM excitation by hyperaccretion requires a significant amount of fine-tuning, and is quite unlikely to occur in nature. Then we summarize and discuss present estimates of black hole QNM excitation from gravitational collapse, distorted black holes and head-on black hole collisions. We emphasize the areas that, in our opinion, are in urgent need of further investigation from the point of view of gravitational wave source modeling.