  We propose emulation of Hawking radiation (HR) by means of acoustic
excitations propagating on top of persistent current in an atomic Bose-Einstein
condensate (BEC) loaded in an annular confining potential. The setting is
initially created as a spatially uniform one, and then switches into a
nonuniform configuration, while maintaining uniform BEC density. The eventual
setting admits the realization of sonic black and white event horizons with
different slopes of the local sound speed. A smooth slope near the white-hole
horizon suppresses instabilities in the supersonic region. It is found that
tongue-shaped patterns of the density-density correlation function, which
represent the acoustic analog of HR, are strongly affected by the radius of the
ring-shaped configuration and number of discrete acoustic modes admitted by it.
There is a minimum radius that enables the emulation of HR. We also briefly
discuss a possible similarity of properties of the matter-wave sonic black
holes to the known puzzle of the stability of Planck-scale primordial black
holes in quantum gravity.

Quantum Gases