Production of irregularly repeating tidal disruption events around massive black holes via diffusive dynamical tides

Tidal disruptions of stars passing near a massive black hole can result in bright high-energy transient signals. For a donor star moving in a bounded orbit with moderately high eccentricity (0.9< e< 0.999), it may survive after a partial disruption and orbit multiple times, causing repeating partial tidal disruption events (rpTDEs). The usual assumption behind an rpTDE is that the donor loses mass every pericenter passage. However, such a picture has difficulties explaining some observed repeating bursts with irregular recurrence times that vary by more than 30%. In this talk, I will present a new mechanism to produce irregular rpTDEs based on dynamical tide-induced mass transfer. This model applies to systems where the pericenter separations are greater than those for mass loss to occur in a single pericenter passage. Nonetheless, the dynamical tide can build up in a diffusive manner over multiple orbits due to a combination of tidal back-reaction, nonlinear anharmonicity, and gravitational wave-driven orbital decay. Eventually, the tidal energy grows close to the donor's binding energy, triggering nonlinear instabilities that eject mass from the donor and power rpTDEs. The time between consecutive bursts in our model is set by the time for the dynamical tide to grow diffusively to the break-up threshold, which naturally produces the irregularity and large variations in the recurrence time of some observed rpTDEs.