Gravitational waves and X-ray signals from stellar disruption by a massive black hole

Gravitational waves and X-ray flares are expected from tidal disruption of stars by a massive black hole. Using a relativistic smoothed particle hydrodynamics code, we investigate the fate of main-sequence and helium stars in plunge orbits passing near Schwarzschild or Kerr black holes of mass ∼10⁵-10⁶ M_⊙. We show that quadrupole gravitational waves emitted during the tidal disruption process are described reasonably well by a point-particle approximation even in the strong-encounter case. An additional hydrodynamic calculation based on the Godunov method indicates that shocks develop for sufficiently high tidal compressions. The shock heating results in an X-ray flare, which for solar-type stars disrupted by ∼10⁶ M_⊙ black holes is in the keV range associated with the gravitational wave signal. The hardness and duration of the X-ray flare may serve as a diagnostic of the mass of the central black hole.