Analog Schwarzschild black hole from a nonisentropic fluid

Abstract

We study the conditions under which an analog acoustic geometry of a relativistic fluid in flat spacetime can take the same form as the Schwarzschild black hole geometry. We find that the speed of sound must necessarily be equal to the speed of light. Since the speed of the fluid cannot exceed the speed of light, this implies that analog Schwarzschild geometry necessarily breaks down behind the horizon.

8 pages, minor revision, discussion on previous works expanded, conclusions expanded, typos corrected, results unchanged