  We propose a simple experiment to create a sonic horizon in isotropically
trapped cold atoms within currently available experimental techniques.
Numerical simulation of the Gross-Pitaevskii equation shows that the sonic
horizon should appear by making the condensate expand. The expansion is
triggered by changing the interaction which can be controlled by the Feshbach
resonance in real experiments. The sonic horizon is shown to be quasi-static
for sufficiently strong interaction or large number of atoms. The
characteristic temperature that is associated with particle emission from the
horizon, which corresponds to the Hawking temperature in an ideal situation, is
estimated to be a few nK.
