Tidal disruption of planetary bodies by white dwarfs – II. Debris disc structure and ejected interstellar asteroids

Abstract

We make use of a new hybrid method to simulate the long-term, multiple-orbit disc formation through tidal disruptions of rocky bodies by white dwarfs, at high-resolution and realistic semi-major axis. We perform the largest-yet suite of simulations for dwarf and terrestrial planets, spanning four orders of magnitude in mass, various pericentre distances and semi-major axes between 3 AU and 150 AU. This large phase space of tidal disruption conditions has not been accessible through the use of previous codes. We analyse the statistical and structural properties of the emerging debris discs, as well as the ejected unbound debris contributing to the population of interstellar asteroids. Unlike previous tidal disruption studies of small asteroids which form ring-like structures on the original orbit, we find that the tidal disruption of larger bodies usually forms dispersed structures of interlaced elliptic eccentric annuli on tighter orbits. We characterize the (typically power-law) size-distribution of the ejected interstellar bodies as well as their composition, rotation velocities and ejection velocities. We find them to be sensitive to the depth (impact parameter) of the tidal disruption. Finally, we briefly discuss possible implications of our results in explaining the peculiar variability of Tabby's star, the origin of the transit events of ZTF J0139+5245 and the formation of a planetary core around SDSS J1228+1040.

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

“…The diagonal line featuring escape shows some instances of collisions occurring between the asteroid and planet. The escape speeds at the Hill surface along the white dwarf phase are all between about 0.01 km/s and 1 km/s, a range that helps distinguish the origin of this escape from other origins (Rafikov 2018;Malamud & Perets 2020b;Pfalzner et al 2021). Instabilities occur throughout the simulations, and are likely to continue at older cooling ages.…”

“…(b) In the more likely case that the debris disc is of comparable or smaller mass compared to the subsequent injected asteroid, then full circularization of the tidal stream is an impossibility. Malamud et al (2021) however showed that the outcome then would be the complete dispersal of the pre-existing compact disc, while the tidal stream undergoes partial circularization only. Even if the mass of the tidal stream exceeds the pre-existing compact disc mass by up 3-5 orders of magnitude (see Equation 8in Malamud et al 2021), significant partial circularization is still possible.…”

“…Circularization can take place without a pre-existing compact disc in the vicinity of the white dwarf -as will be discussed in the next subsections -or indeed with the influence of such a disc, as will be discussed now. Previous studies by Jura (2008) and more recently O'Connor & Lai (2020) and Malamud et al (2021) considered the physical effects which a pre-existing compact disc near the white dwarf might have on the tidal fragments crossing it (in terms of fragment erosion or orbital circularization). The former two studies focused on gaseous compact discs while Malamud et al (2021) broadly discussed gaseous as well as dusty compact discs.…”

“…The study by Malamud et al (2021) identified two possibilities: (a) Suppose a massive asteroid forms an unusually massive compact disc around the white dwarf, and subsequently a typical-mass asteroid then crosses this disc. The interaction between the ensuing tidal stream and compact disc would lead to rapid and full circularization of the tidal fragments, and in particular faster circularization for the smaller fragments, for which drag-assisted circularization is more effective.…”

“…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.…”