Gravitational interactions of stars with supermassive black hole binaries - I. Tidal disruption events

Stars approaching supermassive black holes (SMBHs) in the centres of galaxies can be torn apart by strong tidal forces. We study the physics of tidal disruption by a circular, binary SMBH as a function of the binary mass ratio q = M-2/M-1 and separation alpha, exploring a large set of points in the parameter range q is an element of[0.01, 1] and alpha/r(t1) is an element of[10, 1000]. We simulate encounters in which field stars approach the binary from the loss cone on parabolic, low angular momentum orbits. We present the rate of disruption and the orbital properties of the disrupted stars, and examine the fallback dynamics of the post-disruption debris in the 'frozen-in' approximation. We conclude by calculating the time-dependent disruption rate over the lifetime of the binary. Throughout, we use a primary mass M-1 = 10(6) M-circle dot as our central example. We find that the tidal disruption rate is a factor of similar to 2-7 times larger than the rate for an isolated BH, and is independent of q for q greater than or similar to 0.2. In the 'frozen-in' model, disruptions from close, nearly equal mass binaries can produce intense tidal fallbacks: for binaries with q greater than or similar to 0.2 and alpha/r(t1) similar to 100, roughly similar to 18-40 per cent of disruptions will have short rise times (t(rise) similar to 1-10 d) and highly super-Eddington peak return rates (M-peak/M-Edd similar to 2 x 10(2)-3 x 10(3)).