Tidal disruption of planetary bodies by white dwarfs I: a hybrid sph-analytical approach

Abstract

We introduce a new hybrid method to perform high-resolution tidal disruption simulations, at arbitrary orbits. An SPH code is used to simulate tidal disruptions only in the immediate spatial domain of the star, namely, where the tidal forces dominate over gravity, and then during the fragmentation phase in which the emerging tidal stream may collapse under its own gravity to form fragments. Following each hydrodynamical simulation, an analytical treatment is then applied to instantaneously transfer each fragment back to the tidal sphere for its subsequent disruption, in an iterative process. We validate the hybrid model by comparing it to both an analytical impulse approximation model of single tidal disruptions, as well as full-scale SPH simulations spanning the entire disc formation. The hybrid simulations are essentially indistinguishable from the full-scale SPH simulations, while computationally outperforming their counterparts by orders of magnitude. Thereby our new hybrid approach uniquely enables us to follow the long-term formation and continuous tidal disruption of the planet/planetesimal debris, without the resolution and orbital configuration limitation of previous studies. In addition, we describe a variety of future directions and applications for our hybrid model, which is in principle applicable to any star, not merely white dwarfs.

The dust never settles: collisional production of gas and dust in evolved planetary systems

“…The trend to larger variation on longer, year to decade time-scales is potentially an indicator of orbiting planet(esimal)s or their disrupted fragments. If dust-producing bodies are distributed inhomogeneously along their orbit, as in recent simulations of tidal disruption events (Malamud & Perets 2020a;see also Hahn & Rettig 1998), the time-scale of infrared variation may be an indicator of the orbital period. For example, as discussed by Nixon et al (2020), an eccentric ring of debris may have a semimajor axis that implies the bulk of dust is too cool for detection, yet passes sufficiently close to the star to cause 1000-K dust emission.…”

How Jupiters Save or Destroy Inner Neptunes around Evolved Stars

“…Roughly 5 per cent of these white dwarfs show a detectable infrared excess indicative of the presence of a circumstellar debris disk (Barber et al 2012), and about the same fraction of the latter show a detectable gaseous disk component (Manser et al 2020). As first suggested by Jura (2003), metal polluted white dwarfs and the disks around them are the result of the tidal disruption of rocky planetary material (Veras et al 2014;Malamud & Perets 2020). In the spectacular case of the transiting and disintegrating planetesimal around WD 1145+017 we can witness this process in real time (Vanderburg et al 2015;Gänsicke et al 2016).…”

The entry geometry and velocity of planetary debris into the Roche sphere of a white dwarf

“…Following a tidal disruption of the asteroid, analytical arguments in Malamud & Perets (2020a) constrain the semimajor axes of the ensuing tidal fragments. They could occupy a range of semimajor axes based on the precise origin and size of the asteroid in consideration.…”

“…Kilometre-sized asteroids with a similar range of semimajor axes have always been assumed to tidally disrupt and form a ring with a similar semimajor axis. Such a ring would have a very tiny spread in the orbital energies of the fragments (Veras et al 2014c;Malamud & Perets 2020a;Nixon et al 2020).…”

“…These geometric details are crucial. They determine the type of debris structure formed (Malamud & Perets 2020a), the subsequent evolution of the rings and discs (Bochkarev & Rafikov 2011;Rafikov 2011a,b;Rafikov & Garmilla 2012;Kenyon & Bromley 2017a,b;Miranda & Rafikov 2018;Veras & Heng 2020;Malamud et al 2021;Rozner et al 2021;Trevascus et al 2021) and, ultimately, the accretion rates onto the photosphere. These rates are then used to reconstruct the chemical composition of the destroyed progenitor (e.g.…”