Acoustic clouds: Standing sound waves around a black hole analogue

Abstract

Under certain conditions sound waves in fluids experience an acoustic horizon with analogue properties to those of a black hole event horizon. In particular, a draining bathtub-like model can give rise to a rotating acoustic horizon and hence a rotating black hole (acoustic) analogue. We show that sound waves, when enclosed in a cylindrical cavity, can form stationary waves around such rotating acoustic holes. These acoustic perturbations display similar properties to the scalar clouds that have been studied around Kerr and Kerr-Newman black holes; thus they are dubbed acoustic clouds. We make the comparison between scalar clouds around Kerr black holes and acoustic clouds around the draining bathtub explicit by studying also the properties of scalar clouds around Kerr black holes enclosed in a cavity. Acoustic clouds suggest the possibility of testing, experimentally, the existence and properties of black hole clouds, using analog models.

Synchronized stationary clouds in a static fluid

“…Nonetheless, analogue BHs [34,35], being reproducible in the laboratory, can be encompassed by a reflective surface, as discussed in Ref. [13] (see also Ref. [36], which shows that non-zero vorticity can act as an effective mass term, thus allowing quasibound states to appear in vortex flows).…”

“…Here, building on the ideas of Refs. [13,41] we analyze the possibility of using water waves to set up a laboratory experiment to observe, for the first time, synchronized stationary clouds.…”

Maxwell perturbations on Kerr–anti–de Sitter black holes: Quasinormal modes, superradiant instabilities, and vector clouds

“…They exist at the threshold of the superradiant instabilities triggered by that test field. Recently, a considerable number of studies of such clouds has appeared in the literature, mostly in asymptotically flat spacetimes [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], but also in asymptotically AdS spacetimes [5,7]. 2 Most of these studies have addressed scalar field clouds 3 (even though marginal clouds [30] have been considered for a Proca field [31] in a charged BH background).…”

Ergoregion instability of a rotating quantum system

“…The density profile of the BEC may be determined directly from Eq. (19) [in the Thomas-Fermi approximation], being…”

“…Acoustic analogue systems have shown to be interesting alternatives to investigate (theoretically and experimentally) some properties of compact objects [1][2][3][4][5], as black holes, which so far cannot be subject to experimental reproduction in laboratory. Among the properties that can be studied in acoustic analogue systems, stand out: absorption and scattering of waves [6][7][8][9], quasinormal modes [10][11][12][13], ergoregion instability [14][15][16][17], and stationary configurations [18,19]. Acoustic analogues have been studied in various systems, among which we can mention the perfect fluids and Bose-Einstein condensates (BECs) [20][21][22], the latter being shown as a fruitful proposal of an experimental setup.…”