thermal, with temperature, $T = 62 \, \mathrm{ nK }\, M_{\odot} / M$, for a spherical black hole of mass $M$, where $M_{\odot}$ is the mass of the Sun. Such low temperature Hawking radiation (HR) from solar mass or larger black holes will likely never be observed. However, sonic analogs of HR can exist in hydrodynamic systems possessing a “sonic horizon," where the flow transitions from subsonic to supersonic [@unruh1981]. In such systems, the Hawking temperature is proportional to Planck’s constant times the velocity gradient at the horizon. To produce observable [*quantum*]{} HR, the system must not be much warmer than this temperature, and for this reason Bose-Einstein condensates (BECs) are a natural candidate [@robertson2012; @PhysRevD.85.024021; @PhysRevA.80.043601; @Gardiner2007; @PhysRevLett.113.090405; @PhysRevLett.85.4643]. In a sonic analog, the experimenter has access to the regions both inside and outside of the horizon, thus enabling measurements of correlations that could exhibit quantum entanglement of Hawking quanta and their interior partners [@Balbinot:2007de; @PhysRevA.80.043603; @PhysRevA.85.013621; @Boiron2015; @Steinhauer:2015saa; @Steinhauer:2015ava].

![image](bhwh_030717){width="7.2in"}

In 2014, Steinhauer [@nphys3104] reported on a remarkable experiment that implements a sonic analog black hole in a needle–shaped BEC of $^{87}$Rb. The BEC is swept by a negative step potential with the energy equivalent of a few 