Near the Horizon of a Sonic Black-Hole


Jonathan Curtis (JQI and CMTC)
Friday, February 9 2018 at 4:00 pm
PSC 2136

*Snacks and drinks at 4 pm, talk at 4:10 pm*

When the quantum behavior of matter is accounted for, black-holes become thermal black-bodies rather than the perfect absorbers they are classically envisioned to be. This emission of thermal radiation eventually causes the black-hole to evaporate away [1].
An analogous process happens in fluids which flow faster than the local speed of sound. For classical fluids, transport processes can only flow downstream once the sonic event-horizon is passed. In quantum fluids (e.g. a BEC) a supersonic flow is generally accompanied by the thermal emission of phonons, a process analogous to Hawking radiation. This analogy can be made more rigorous, where it is shown that for a slowly varying condensate a flux of thermally populated phonons appears once the speed of sound is crossed [2].

We study the extreme limit of this system where the fluid is made to drastically jump from a subsonic flow to a supersonic flow. This “step-like” problem can be formulated in terms of a one-dimensional wave-equation which describes the rate at which Hawking particles are emitted. We find that, in contrast to the far-field behavior which looks universally thermal, the near-horizon field has significant departures from the thermal description. This departure can be understood as arising from quantum interference between outgoing phonons and trapped phonons partially tunneling out of the black-hole. We briefly discuss how this process fits into the existing understanding of the “black-hole information paradox.”

J.B. Curtis, G. Refael, V. Galitski, “Evanescent Horizon Modes Partnered to Acoustic Hawking Emission,” (2018) arXiv:1801.01607

[1] S.W. Hawking, “Black hole explosions?” Nature 248 30 (1974)  
[2] W.G. Unruh, “Experimental Black-Hole Evaporation?” Phys. Rev. Lett. 46 21 (1981)