Exoplanet recycling in massive white-dwarf debris discs
Lieshout, Rik van
Monthly Notices of the Royal Astronomical Society
Oxford University Press
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Lieshout, R. v., Kral, Q., Charnoz, S., Wyatt, M., & Shannon, A. (2018). Exoplanet recycling in massive white-dwarf debris discs. Monthly Notices of the Royal Astronomical Society, 480 (2), 2784-2812. https://doi.org/10.1093/mnras/sty1271
Several tens of white dwarfs are known to host circumstellar discs of dusty debris, thought to arise from the tidal disruption of rocky bodies originating in the star’s remnant planetary system. This paper investigates the evolution of such discs if they are very massive, as may be the case if their progenitor was a terrestrial planet, moon, or dwarf planet. Assuming the discs are physically thin and flat, like Saturn’s rings, their evolution is governed by Poynting–Robertson drag or viscous spreading, where the disc’s effective viscosity is due to self-gravity wakes. For discs with masses ≳ 1026 g, located in the outer parts of the tidal disruption zone, viscous spreading dominates the evolution, and mass is transported both in- and outwards. When outwards-spreading material flows beyond the Roche limit, it coagulates into new (minor) planets in a process analogous to the ongoing formation of moonlets at the outer edge of Saturn’s rings. The newly formed bodies migrate outwards by exchanging angular momentum with the disc and coalesce into larger objects through mutual collisions. Eventually, the disc’s Roche-limit overflow recycles tens of percent of the original disc mass; most ends up in a single large body near 2:1 mean-motion resonance with the disc’s outer edge. Hence, the recycling of a tidally disrupted super-Earth, for example, could yield an Earth-mass planet on a ∼10-h orbit, located in the habitable zone for 2-to-10-Gyr-old white dwarfs. The recycling process also creates a population of smaller bodies just outside the Roche limit, which may explain the minor planets recently postulated to orbit WD 1145+017.
accretion, accretion discs, planets and satellites: formation, planet-disc interactions, planet-star interactions, stars: individual: WD 1145+017, white dwarfs
RvL, QK, MCW, and AS acknowledge support from the European Union through ERC grant number 279973. RvL is also supported by the DISCSIM project, grant agreement 341137 funded by the European Research Council under ERC-2013-ADG. QK acknowledges funding from STFC via the Institute of Astronomy, Cambridge Consolidated Grant. AS is partially supported by funding from the Center for Exoplanets and Habitable Worlds. The Center for Exoplanets and Habitable Worlds is supported by the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium.
European Research Council (279973)
European Research Council (341137)
SCIENCE & TECHNOLOGY FACILITIES COUNCIL (ST/N000927/1)
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External DOI: https://doi.org/10.1093/mnras/sty1271
This record's URL: https://www.repository.cam.ac.uk/handle/1810/279774