Tidal disruption events (TDEs) originated from black hole (BH)-white dwarf (WD) systems not only produce signals of low-frequency gravitational waves (GWs), $\gamma$-rays, and supernovas Ia-like but also associate with BH ultracompact x-ray binaries (UCXBs). Based on a semianalytical method, we systematically investigate the formation of TDEs evolving from stellar-mass BH-WD systems. Our simulations show that, for those BH-WD systems with initial orbital periods shorter than critical periods, GW radiation always dominates the orbital evolution after they evolve into UCXBs, driving those systems to experience a continuous orbital decay and eventually trigger TDEs. BH UCXBs can appear as ultraluminous x-ray sources and low-frequency GW sources with high signal-to-noise ratios prior to TDEs, which provide multimessenger signals to pursue follow-up observations of TDEs in Local Group of Galaxies. We also obtain an initial parameter space of BH-WD binaries as the progenitors of TDEs in the WD masses and orbital periods plane, which can be applied to future population synthesis simulations.

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• Formation & evolution of stars & galaxies