A dark year for tidal disruption events
Main-sequence disruptions of stars by supermassive black holes result in the production of an extended, geometrically thin debris stream winding repeatedly around the black hole. In the absence of black hole spin, in-plane relativistic precession causes this stream to intersect with itself after a single winding. In this paper we show that relativistic precessions arising from black hole spin can induce deflections out of the original orbital plane that prevent the stream from self-intersecting even after many windings. This naturally leads to a “dark period” in which the flare is not observable for some time, persisting for up to a dozen orbital periods of the most bound material, which translates to years for disruptions around black holes with masses ∼10{sup 7}M{sub ⊙}. When the stream eventually self-intersects, the distance from the black hole and the angle at which this collision occurs determine the rate of energy dissipation. We find that more-massive black holes (M{sub h}≳10{sup 7}M{sub ⊙}) tend to have more violent stream self-intersections, resulting in prompt accretion. For these tidal disruption events (TDEs), the accretion rate onto the black hole should still closely follow the original fallback rate after a fixed delay time t{sub delay}, M-dot {sub acc}(t+t{sub delay})= M-dot {sub fb}(t). For lower black hole masses (M{sub h}≲10{sup 6}), we find that flares are typically slowed down by about an order of magnitude, resulting in the majority of TDEs being sub-Eddington at peak. This also implies that current searches for TDEs are biased toward prompt flares, with slowed flares likely having been unidentified.