Can Giant Planets Form by Direct Gravitational Instability?

By R. Rafikov. 2004

321 citations recorded by the source corpus.

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 103 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 (~10MJ) 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.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/7f91647f391d302c79792cd759200519f02ac602

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Citations in the corpus

Dynamics of Protoplanetary Disks (2010, background): “A central result of such simplified models is that fragmentation cannot occur in the inner disk (Rafikov 2005).”
THE RUNTS OF THE LITTER: WHY PLANETS FORMED THROUGH GRAVITATIONAL INSTABILITY CAN ONLY BE FAILED BINARY STARS (2009, methodology): “While GI is an unlikely formation mechanism for close in planets (Rafikov 2005), for more widely separated planets, or sub-stellar companions, the viability GI-driven fragmentation deserves further investigation.”
Rapid growth of gas-giant cores by pebble accretion (2012, background): “Additionally, at smaller stellar separations, gas cools too slowly for the spiral arms to fragment into bound clumps (Matzner & Levin 2005; Rafikov 2005).”
The importance of radiative feedback for the stellar initial mass function (2008, background): “Rafikov (2005), Matzner & Levin (2005), Kratter & Matzner (2006), and Whitworth & Stamatellos (2006) have all pointed out that accurate treatments of radiative transfer are likely to significantly decrease disc fragmentation.”
THE TWO MODES OF GAS GIANT PLANET FORMATION (2009, background): “…(GIs) to form gas giants directly, the Toomre (1964) Q = csκ/πGΣ, where cs is the sound speed, κ is the epicyclic frequency, and Σ is the surface density, must approach unity and the local cooling time must be . the local orbit period (Gammie 2001; Rice et al. 2005; Rafikov 2005, 2007).”
THE FORMATION MECHANISM OF GAS GIANTS ON WIDE ORBITS (2009, unknown): “20– 40 AU (Rafikov 2005; Boley & Durisen 2008; Stamatellos & Whitworth 2008; Cai et al. 2009; Forgan et al. 2009), it does occur in extended disks outside of a few tens of AU (Boley 2009; Stamatellos & Whitworth 2009) provided that the disks are massive.”
The planet nine hypothesis (2019, background): “…of the early solar nebula provides an alternate means of forming planets, it is irrelevant to the problem at hand, since the mass scale for objects generated through this channel is of order 10 MJ (or higher, e.g., Rafikov 2005) may have occupied the outer solar system during its infancy.”
The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation (2008, background): “Fragmentation is also unlikely to happen close to the urstar (e.g. Matzner & Levin 2005; Rafikov 2005; Whitworth & Stamatellos 2006; Boley et al. 2006; Durisen et al. 2007; Stamatellos et al. 2007b; Stamatellos & Whitworth 2008; Cai et al. 2008).”
THE FORMATION OF LOW-MASS BINARY STAR SYSTEMS VIA TURBULENT FRAGMENTATION (2010, background): “Otherwise disks become unstable outside of a much smaller radius, within which cooling times are too long and viscous heating alone suffices to suppress fragmentation (Rafikov 2005; Matzner & Levin 2005; Clarke 2009)”
Rapid inward migration of planets formed by gravitational instability (2011, background): “It is thought to operate at separations larger than 30−50 AU from the central (Sun-like) star (e.g., Rafikov 2005; Matzner & Levin 2005; Stamatellos & Whitworth 2008).”
A COMBINED SUBARU/VLT/MMT 1–5 μm STUDY OF PLANETS ORBITING HR 8799: IMPLICATIONS FOR ATMOSPHERIC PROPERTIES, MASSES, AND FORMATION (2011, background): “Core accretion preferentially forms planets with smaller masses and orbital separations, while disk instability has difficulty producing lower-mass gas giants and forming them close to the star (e.g. Rafikov 2005; Kratter et al. 2010).”
Formation of Giant Planets (2004, background): “Additionally, due to inefficient cooling, both analytic arguments and numerical simulations indicate that the possibilities of fragmenting a disk inside several tens of AU appear remote under reasonable circumstances (e.g., Rafikov 2005; Rogers and Wadsley 2011; Durisen 2011).”
THE BURST MODE OF ACCRETION AND DISK FRAGMENTATION IN THE EARLY EMBEDDED STAGES OF STAR FORMATION (2010, background): “This criterion, along with G ≤ 1–3, is often invoked when analyzing the disk susceptibility to fragmentation (e.g. Rafikov 2005).”
Stellar, brown dwarf and multiple star properties from hydrodynamical simulations of star cluster formation (2008, background): “Rafikov (2005), Matzner & Levin (2005), Kratter & Matzner (2006), and Whitworth & Stamatellos (2006) have all pointed out that accurate treatments of radiative transfer are likely to significantly decrease disc fragmentation.”
Black hole mergers: can gas discs solve the ‘final parsec’ problem? (2009, background): “In protostellar accretion discs the parameterβ is generally much larger than unity (Rafikov 2005).”
A companion to AB Pic at the planet/brown dwarf boundary (2005, background): “Gravitational instabilities within a protoplanetary disk (Papaloizou & Terquem 2001; Rafikov 2005) or mechanisms proposed for brown dwarfs formation (Kroupa & Bouvier 2003) appear to be more probable scenarii to explain the origin of wide companions such as AB Pic b. Interestingly, gravitational…”