Spectral properties of acoustic black hole radiation: Broadening the horizon

TL;DR

This paper investigates how short-distance dispersion affects the spectrum of acoustic black hole radiation in Bose condensates, revealing that the effective temperature depends on an averaged flow gradient, indicating horizon broadening.

Contribution

It introduces a model showing that horizon broadening influences the black hole spectrum's temperature, extending understanding of dispersive effects in analogue gravity systems.

Findings

Spectrum remains nearly Planckian despite dispersion effects.

Temperature depends on the average flow gradient over a broadened horizon.

Nonadiabatic effects can cause oscillations or flux amplification.

Abstract

The sensitivity of the black hole spectrum when introducing short distance dispersion is studied in the context of atomic Bose condensates. By considering flows characterized by several length scales, we show that, while the spectrum remains remarkably Planckian, the temperature is no longer fixed by the surface gravity. Rather it is determined by the average of the flow gradient across the horizon over an interval fixed by the healing length and the surface gravity, as if the horizon were broadened. This remains valid as long as the flow does not induce nonadiabatic effects that produce oscillations or some parametric amplification of the flux.