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

Debojyoti GarainTapobrata Sarkar
Jan 2024
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 ($\gtrsim 10^{5-6} M_{\odot}$) black holes. Observational signatures of these can result from tidal disruption of white dwarfs (WDs), which would otherwise be captured as a whole by super-massive black holes. 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 black hole 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. We find substantial effects of the ``coupling'' between the black hole spin and the spin of the white dwarf, although the pericenter distance of the white dwarf is taken to be large enough so that the Newtonian limit of its fluid dynamics is a robust approximation. In particular, the core mass, the bound tail mass, and the mass difference between the two tidal tails strongly depend on such ``coupled'' spin effects. However, the late time fallback rate of the debris behaves similar to the non-spinning cases. We also compute gravitational wave amplitudes and find that while the black hole spin influences the same, there is no evidence of influence of stellar spin on such amplitudes in our regime of interest.
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