Horizon hair of extremal black holes and measurements at null infinity

TL;DR

This paper demonstrates that conserved charges related to scalar perturbations on extremal black holes can be measured from null infinity, offering potential observational signatures through precise late-time asymptotics of outgoing radiation.

Contribution

It proves that conserved charges on extremal black hole horizons are externally measurable from null infinity, linking theoretical properties to potential observations.

Findings

Conserved charges are measurable from null infinity.

Late-time asymptotics of radiation fields are precisely characterized.

Potential observational signatures for extremal black holes are identified.

Abstract

It is shown that the conserved charges on the event horizon and the Cauchy horizon associated to scalar perturbations on extremal black holes are externally measurable from null infinity. This suggests that these charges have the potential to serve as an observational signature. The proof of this result is based on obtaining precise late-time asymptotics for the radiation field of outgoing perturbations.