Partial tidal disruptions of spinning eccentric white dwarfs by spinning intermediate mass black holes

Abstract

Intermediate-mass black holes (IMBHs, $\sim 10^2-10^5M_{\odot}$) are often dubbed as the missing link between stellar mass ($\lesssim 10^2M_{\odot}$) and super-massive ($\gtrsim 10^{5-6} M_{\odot}$) BHs. Observational signatures of these can result from tidal disruptions of white dwarfs (WDs), which would otherwise be captured as a whole by super-massive BHs. Recent observations indicate that IMBHs might be rapidly spinning, while it is also known that isolated white dwarfs might have large spins, with spin periods of the order of minutes. Here, we aim to understand the effects of ``coupling'' between BH and stellar spin, focussing on the tidal disruption of spinning WDs in the background of spinning IMBHs. Using smoothed particle hydrodynamics, we perform a suite of numerical simulations of partial tidal disruptions, where spinning WDs are in eccentric orbits about spinning IMBHs. We take a hybrid approach, where we integrate the Kerr geodesic equations while being in a regime where we can treat the internal stellar fluid dynamics in the Newtonian limit. The coupling of BH and stellar spin results in distinctive behaviour of mass distribution of debris, compared to non-rotating cases. Further, while late time fallback rates of debris into the BH is unaffected by only BH spin, these have noticeable deviations in the presence of stellar spin, in particular, this causes a broadening of the fallback curves at late times. On the other hand, gravitational wave signatures are unaffected by stellar spin in the parameter regime that we consider.