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Accretion of tidally disrupted asteroids on to white dwarfs : Direct accretion versus disc processing

Li, Daohai LU orcid ; Mustill, Alexander J. LU orcid and Davies, Melvyn B. LU (2021) In Monthly Notices of the Royal Astronomical Society 508(4). p.5671-5686
Abstract

Atmospheric heavy elements have been observed in more than a quarter of white dwarfs (WDs) at different cooling ages, indicating ongoing accretion of asteroidal material, whilst only a few per cent of the WDs possess a dust disc, and all these WDs are accreting metals. Here, assuming that a rubble-pile asteroid is scattered inside a WD's Roche lobe by a planet, we study its tidal disruption and the long-Term evolution of the resulting fragments. We find that after a few pericentric passages, the asteroid is shredded into its constituent particles, forming a flat, thin ring. On a time-scale of Myr, tens of per cent of the particles are scattered on to the WD, and are therefore directly accreted without first passing through a... (More)

Atmospheric heavy elements have been observed in more than a quarter of white dwarfs (WDs) at different cooling ages, indicating ongoing accretion of asteroidal material, whilst only a few per cent of the WDs possess a dust disc, and all these WDs are accreting metals. Here, assuming that a rubble-pile asteroid is scattered inside a WD's Roche lobe by a planet, we study its tidal disruption and the long-Term evolution of the resulting fragments. We find that after a few pericentric passages, the asteroid is shredded into its constituent particles, forming a flat, thin ring. On a time-scale of Myr, tens of per cent of the particles are scattered on to the WD, and are therefore directly accreted without first passing through a circularized close-in disc. Fragment mutual collisions are most effective for coplanar fragments, and are thus only important in 103-104 yr before the orbital coplanarity is broken by the planet. We show that for a rubble pile asteroid with a size frequency distribution of the component particles following that of the near earth objects, it has to be roughly at least 10 km in radius such that enough fragments are generated and $\ge 10{{\ \rm per\ cent}}$ of its mass is lost to mutual collisions. At relative velocities of tens of km s-1, such collisions grind down the tidal fragments into smaller and smaller dust grains. The WD radiation forces may shrink those grains' orbits, forming a dust disc. Tidal disruption of a monolithic asteroid creates large km-size fragments, and only parent bodies ≥100 km are able to generate enough fragments for mutual collisions to be significant. Hence, those large asteroids experience a disc phase before being accreted.

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Please use this url to cite or link to this publication:
author
; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
accretion, accretion discs-planets and satellites: dynamical evolution and stability, methods: numerical, minor planets, asteroids: general, white dwarfs
in
Monthly Notices of the Royal Astronomical Society
volume
508
issue
4
pages
16 pages
publisher
Oxford University Press
external identifiers
  • scopus:85119511958
ISSN
0035-8711
DOI
10.1093/mnras/stab2949
project
IMPACT: Comets, asteroids and the habitability of planets
Wallenberg Academy Fellow Project
A unified picture of white dwarf planetary systems
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
id
6ca46d36-6256-4dc9-bba2-7cdcd7478e07
alternative location
https://arxiv.org/abs/2106.00441
date added to LUP
2021-12-08 21:37:43
date last changed
2024-04-20 17:18:41
@article{6ca46d36-6256-4dc9-bba2-7cdcd7478e07,
  abstract     = {{<p>Atmospheric heavy elements have been observed in more than a quarter of white dwarfs (WDs) at different cooling ages, indicating ongoing accretion of asteroidal material, whilst only a few per cent of the WDs possess a dust disc, and all these WDs are accreting metals. Here, assuming that a rubble-pile asteroid is scattered inside a WD's Roche lobe by a planet, we study its tidal disruption and the long-Term evolution of the resulting fragments. We find that after a few pericentric passages, the asteroid is shredded into its constituent particles, forming a flat, thin ring. On a time-scale of Myr, tens of per cent of the particles are scattered on to the WD, and are therefore directly accreted without first passing through a circularized close-in disc. Fragment mutual collisions are most effective for coplanar fragments, and are thus only important in 103-104 yr before the orbital coplanarity is broken by the planet. We show that for a rubble pile asteroid with a size frequency distribution of the component particles following that of the near earth objects, it has to be roughly at least 10 km in radius such that enough fragments are generated and $\ge 10{{\ \rm per\ cent}}$ of its mass is lost to mutual collisions. At relative velocities of tens of km s-1, such collisions grind down the tidal fragments into smaller and smaller dust grains. The WD radiation forces may shrink those grains' orbits, forming a dust disc. Tidal disruption of a monolithic asteroid creates large km-size fragments, and only parent bodies ≥100 km are able to generate enough fragments for mutual collisions to be significant. Hence, those large asteroids experience a disc phase before being accreted.</p>}},
  author       = {{Li, Daohai and Mustill, Alexander J. and Davies, Melvyn B.}},
  issn         = {{0035-8711}},
  keywords     = {{accretion, accretion discs-planets and satellites: dynamical evolution and stability; methods: numerical; minor planets, asteroids: general; white dwarfs}},
  language     = {{eng}},
  month        = {{12}},
  number       = {{4}},
  pages        = {{5671--5686}},
  publisher    = {{Oxford University Press}},
  series       = {{Monthly Notices of the Royal Astronomical Society}},
  title        = {{Accretion of tidally disrupted asteroids on to white dwarfs : Direct accretion versus disc processing}},
  url          = {{http://dx.doi.org/10.1093/mnras/stab2949}},
  doi          = {{10.1093/mnras/stab2949}},
  volume       = {{508}},
  year         = {{2021}},
}