Did Fomalhaut, HR 8799, and HL Tauri Form Planets via the Gravitational Instability? Placing Limits on the Required Disk Masses

Abstract

Disk fragmentation resulting from the gravitational instability has been proposed as an efficient mechanism for forming giant planets. We use the planet Fomalhaut b, the triple-planetary system HR 8799, and the potential protoplanet associated with HL Tau to test the viability of this mechanism. We choose the above systems since they harbor planets with masses and orbital characteristics favored by the fragmentation mechanism. We do not claim that these planets must have formed as the result of fragmentation, rather the reverse: if planets can form from disk fragmentation, then these systems are consistent with what we should expect to see. We use the orbital characteristics of these recently discovered planets, along with a new technique to more accurately determine the disk cooling times, to place both lower and upper limits on the disk surface density--and thus mass--required to form these objects by disk fragmentation. Our cooling times are over an order of magnitude shorter than those of Rafikov (2005),which makes disk fragmentation more feasible for these objects. We find that the required mass interior to the planet's orbital radius is ~0.1 Msun for Fomalhaut b, the protoplanet orbiting HL Tau, and the outermost planet of HR 8799. The two inner planets of HR 8799 probably could not have formed in situ by disk fragmentation.

5 pages, 1 figure, accepted for publication in ApJL

References in corpus (8)

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• Enhanced Dust Emission in the HL Tau Disc: A Low-Mass Companion in Formation?

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• Formation of Giant Planets by Disk Instability on Wide Orbits Around Protostars with Varied Masses
• Non-convergence of the critical cooling timescale for fragmentation of self-gravitating discs
• A Disk Around the Planetary-Mass Companion GSC 06214-00210 b: Clues About the Formation of Gas Giants on Wide Orbits
• Planets Around Low-Mass Stars (PALMS). III. A Young Dusty L Dwarf Companion at the Deuterium-Burning Limit
• Formation and survivability of giant planets on wide orbits
• The Gemini NICI Planet-Finding Campaign: The Frequency of Giant Planets Around Debris Disk Stars
• On The Possibility of Enrichment and Differentiation in Gas Giants During Birth by Disk Instability
• Thermal Infrared MMTAO Observations of the HR 8799 Planetary System
• The Case of AB Aurigae's Disk in Polarized Light: Is There Truly a Gap?
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• Resolving the Circumstellar Disk of HL Tauri at Millimeter Wavelengths
• Efficiency of thermal relaxation by radiative processes in protoplanetary discs: constraints on hydrodynamic turbulence
• Metallicity of the Massive Protoplanets Around HR 8799 If Formed by Gravitational Instability
• Identifying and Analysing Protostellar Disc Fragments in Smoothed Particle Hydrodynamics Simulations
• Four-of-a-kind? Comprehensive atmospheric characterisation of the HR 8799 planets with VLTI/GRAVITY
• 13C17O suggests gravitational instability in the HL Tau disc
• The fragmentation of protostellar discs: the Hill criterion for spiral arms
• The Dynamical Fate of Self-Gravitating Disc Fragments After Tidal Downsizing
• Giant Planet Formation by Disk Instability in Low Mass Disks?
• The Effect of Protoplanetary Disk Cooling Times on the Formation of Gas Giant Planets by Gravitational Instability
• Binary companions triggering fragmentation in self-gravitating discs
• The evolution of self-gravitating accretion discs
• AB Aurigae: Possible evidence of planet formation through the gravitational instability
• A Lower Angular Momentum Limit for Self-Gravitating Protostellar Disc Fragmentation
• Characterizing fragmentation and sub-Jovian clump properties in magnetized young protoplanetary disks
• The Effect of the Approach to Gas Disk Gravitational Instability on the Rapid Formation of Gas Giant Planets
• Pebble accretion in self-gravitating protostellar discs
• The Outcome of the Protoplanetary Disk of Very Massive Stars