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Cited by 433Astrophysics and Star Formation StudiesAstro and Planetary ScienceStellar, planetary, and galactic studies

Can Giant Planets Form by Direct Gravitational Instability?

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Rafikov, Roman R.·2005·The Astrophysical Journal
DOI 10.1086/428899
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Abstract

Gravitational instability has been invoked as a possible mechanism of the giant planet production in protoplanetary disks. Here we critically revise its viability by noting that to form planets directly, it is not enough for protoplanetary disks to be gravitationally unstable. They must also be able to cool efficiently (on a timescale comparable to the local disk orbital period) to allow the formation of the bound clumps by fragmentation. A combination of the dynamical and thermal constraints puts very stringent lower limits on the properties of disks capable of fragmenting into the self-gravitating objects: for the gravitational instability to form giant planets at 10 AU in the disk cooled by the radiation transfer, the gas temperature must exceed 10 3 K with a minimum disk mass of 0.7 M ☉ and a luminosity of 40 L ☉ . Although these requirements are relaxed in the more distant parts of the disk, masses of the bound objects formed as a result of instability are too large even at 100 AU (~10 M J ) to explain the characteristics of known extrasolar giant planets. Such protoplanetary disks (and planets formed in them) have very unusual observational properties, and this severely constrains the possibility of giant planet formation by direct gravitational instability.

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  • Even if the gas were dense enough for disk fragmentation, at short orbital periods fragments would shear out before they could cool and contract.

    “More importantly, even if the gas were dense enough for disk fragmentation, at short orbital periods fragments would shear out before they could cool and contract.”

    From Origins of Hot Jupiters (2018) · cites this paper as Rafikov 2005

    Section 2, “Dynamical and Thermal Constraints” (page unavailable), says that sufficient gas density alone is not enough: cooling must also be fast enough for fragmentation to produce bound clumps. The paper does not say that already-formed fragments shear out before contracting, and it treats fragmentation at small radii as subject to stringent cooling and disk-property requirements rather than an unconditional outcome. (LLM, conf=0.83)

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  • Such high temperatures would unbind the gas from the star, so conditions for gravitational instability close to the star are not expected.

    “As argued by Rafikov (2005), such high temperatures would unbind the gas from the star. Therefore we do not expect the conditions for gravitational instability close to the star.”

    From Origins of Hot Jupiters (2018) · cites this paper as Rafikov 2005

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Research works printed but not linked: 2

  1. Levin, Yu. 2003, preprint (astro-ph/0307084) · arXiv
  2. Rafikov, R. R. 2004a, AJ, 128, 1348 ---. 2004b, ApJ, submitted (astro-ph/0405507) · arXiv

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Authors
Rafikov, R. R.
Corresponding author
Rafikov, Roman R.
ORCID
Rafikov, Roman R.
Venue
The Astrophysical Journal
Publisher
American Astronomical Society
Published
2005-01-31
Volume
621
Issue
1
Pages
L69-L72
ISSN
  • 0004-637X (ISSN-L)
  • 1538-4357
DOI
10.1086/428899
OpenAlex
W2064514018
Cited by
433
References
20
Citations by year
2026: 11 · 2025: 17 · 2024: 10 · 2023: 8 · 2022: 12 · 2021: 19 · 2020: 17 · 2019: 22 · 2018: 44 · 2017: 15 · 2016: 39 · 2015: 17 · 2014: 14 · 2013: 19 · 2012: 26
FWCI
10.85
Type
journal article
Language
en
Open access
Locations
  • The Astrophysical Journal (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • CERN Document Server (European Organization for Nuclear Research) (submittedVersion)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysics and Star Formation Studies
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astro and Planetary Science
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Stellar, planetary, and galactic studies
Keywords
giant planet formation, gravitational instability, protoplanetary disks, disk fragmentation, disk cooling, extrasolar giant planets, gas temperature

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