The Endgame of Gas Giant Formation: Accretion Luminosity and Contraction Post-Runaway

Abstract

Giant planets are thought to form by runaway gas accretion onto solid cores. Growth must eventually stop running away, ostensibly because planets open gaps (annular cavities) in their surrounding discs. Typical models stop runaway by artificially capping the accretion rate and lowering it to zero over an arbitrarily short time-scale. In reality, post-runaway accretion persists as long as the disc remains. During this final and possibly longest phase of formation, when the planet is still emerging from the disc, its mass can more than double, and its radius contracts by orders of magnitude. By drawing from the theory of how gaps clear, we find that post-runaway accretion luminosities diverge depending on disc viscosity: luminosities fall in low-viscosity discs but continue to rise past runaway in high-viscosity discs. This divergence amounts to a factor of $10^2$ by the time the disc disperses. Irrespective of the specifics of how planets interact with discs, the observed luminosity and age of an accreting planet can be used to calculate its instantaneous mass, radius, and accretion rate. We perform this exercise for the planet candidates embedded within the discs orbiting PDS 70, HD 163296, and MWC 758, inferring masses of $1-10M_{\mathrm{J}}$, accretion rates of $0.1-10M_{\mathrm{J}}$/Myr, and radii of $1-10R_{\mathrm{J}}$. Our radii are computed self-consistently from the planet's concurrent contraction and accretion and do not necessarily equal the value of $2R_{\mathrm{J}}$ commonly assumed; in particular, the radius depends on the envelope opacity as $R\propto {\kappa }^{0.5}$.

arXiv commentAccepted to MNRAS

References in corpus (65)

• Protoplanetary Disks and Their Evolution
• Using FU Orionis Outbursts to Constrain Self-Regulated Protostellar Disk Models
• Discovery of a planetary-mass companion within the gap of the transition disk around PDS 70
• Accretion Disks Around Young Objects. III. Grain Growth
• On the Luminosity of Young Jupiters
• Line and Mean Opacities for Ultracool Dwarfs and Extrasolar Planets
• The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics From 10-100 AU
• Two accreting protoplanets around the young star PDS 70
• Disk Accretion Onto High-Mass Planets
• Mass Flow and Accretion through gaps in Accretion Discs
• Spectral and Photometric Diagnostics of Giant Planet Formation Scenarios
• A Review of Bondi--Hoyle--Lyttleton Accretion
• Imaging Extrasolar Giant Planets
• Models of the in situ formation of detected extrasolar giant planets
• Atmospheres of protoplanetary cores: critical mass for nucleated instability
• Characterization of exoplanets from their formation I: Models of combined planet formation and evolution
• Planetary Torques as the Viscosity of Protoplanetary Disks
• Accreting Protoplanets in the LkCa 15 Transition Disk
• Super-Earth Atmospheres: Self-Consistent Gas Accretion and Retention
• Breeding Super-Earths and Birthing Super-Puffs in Transitional Disks
• Models of Jupiter's Growth Incorporating Thermal and Hydrodynamic Constraints
• Initial Conditions of Planet Formation: Lifetimes of Primordial Disks
• Orbital Migration and Mass Accretion of Protoplanets in 3D Global Computations with Nested Grids
• Make Super-Earths, Not Jupiters: Accreting Nebular Gas onto Solid Cores at 0.1 AU and Beyond
• Orbital and atmospheric characterization of the planet within the gap of the PDS 70 transition disk
• Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity
• To Cool is to Accrete: Analytic Scalings for Nebular Accretion of Planetary Atmospheres
• On the Minimum Core Mass for Giant Planet Formation at Wide Separations
• Accretion of Jupiter-mass Planets in the Limit of Vanishing Viscosity
• Formation of Jupiter using opacities based on detailed grain physics
• X-shooter spectroscopy of young stellar objects: I - Mass accretion rates of low-mass T Tauri stars in σOrionis
• Accreting Circumplanetary Disks: Observational Signatures
• Magellan Adaptive Optics Imaging of PDS 70: Measuring the Mass Accretion Rate of a Young Giant Planet within a Gapped Disk
• Dynamical Constraints on the HR 8799 Planets with GPI
• The Dispersal of Protoplanetary Disks
• An Atmospheric Structure Equation for Grain Growth
• Final Masses of Giant Planets II: Jupiter Formation in a Gas-Depleted Disk
• Characterization of exoplanets from their formation III: The statistics of planetary luminosities
• Minimum Core Masses for Giant Planet Formation With Realistic Equations of State and Opacities
• Models of Accreting Gas Giant Protoplanets in Protostellar Disks
• On the Terminal Rotation Rates of Giant Planets
• Grain opacity and the bulk composition of extrasolar planets. II. An analytical model for the grain opacity in protoplanetary atmospheres
• Discovery of a point-like source and a third spiral arm in the transition disk around the Herbig Ae star MWC 758
• The mass of the young planet Pictoris b through the astrometric motion of its host star
• No Clear, Direct Evidence for Multiple Protoplanets Orbiting LkCa 15: LkCa 15 bcd are Likely Inner Disk Signals
• VLT/SPHERE exploration of the young multiplanetary system PDS70
• Evidence for a circumplanetary disk around protoplanet PDS 70 b
• The Boundary between Gas-rich and Gas-poor Planets
• A Systematic Study of the Final Masses of Gas Giant Planets
• Evolution of Gas Giant Entropy During Formation by Runaway Accretion
• A Model-Independent Mass and Moderate Eccentricity for $\beta$ Pic b
• Hot-Jupiter Inflation due to Deep Energy Deposition
• Observability of Forming Planets and their Circumplanetary Disks II. -- SEDs and Near-Infrared Fluxes
• Gas Accretion onto a Protoplanet and Formation of a Gas Giant Planet
• The Planetary Accretion Shock: I. Framework for Radiation-hydrodynamical Simulations and First Results
• Separating extended disc features from the protoplanet in PDS 70 using VLT/SINFONI
• The Planetary Accretion Shock. II. Grid of Post-Shock Entropies and Radiative Shock Efficiencies for Non-Equilibrium Radiation Transport
• Physical and radiative properties of the first core accretion shock
• High-contrast imaging of HD 163296 with the Keck/NIRC2 L'-band vortex coronograph
• The End of Runaway: How Gap Opening Limits the Final Masses of Gas Giants
• Spectral Energy Distributions of Accreting Protoplanets
• Young Jupiters are Faint: New Models of the Early Evolution of Giant Planets
• Spectro-astrometry of the pre-transitional star LkCa 15 does not reveal an accreting planet but extended H$\alpha$ emission
• Optically Thin Core Accretion: How Planets Get Their Gas in Nearly Gas-Free Disks
• Deep and wide gaps by super Earths in low-viscosity discs

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• Constraining the Nature of the PDS 70 Protoplanets with VLTI/GRAVITY
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• Keck/NIRC2 $L$'-Band Imaging of Jovian-Mass Accreting Protoplanets around PDS 70
• Heavy-metal Jupiters by major mergers: metallicity vs. mass for giant planets
• How Consumption and Repulsion Set Planetary Gap Depths and the Final Masses of Gas Giants
• The maximum accretion rate of a protoplanet: how fast can runaway be?
• Breaking the centrifugal barrier to giant planet contraction by magnetic disc braking
• ISPY-NACO Imaging Survey for Planets around Young stars. The demographics of forming planets embedded in protoplanetary disks
• Self-consistent modelling of the dust component in protoplanetary and circumplanetary disks: the case of PDS 70
• Inflated Eccentric Migration of Evolving Gas-Giants I: Accelerated Formation and Destruction of Hot and Warm Jupiters
• MIRACLES: atmospheric characterization of directly imaged planets and substellar companions at 4-5 $\mu$m. II. Constraints on the mass and radius of the enshrouded planet PDS 70 b
• Testing planet formation from the ultraviolet to the millimeter
• Searching for Protoplanets around MWC 758 and MWC 480 in Br-$\gamma$ using Kernel Phase and SCExAO/CHARIS
• Dynamical stability of giant planets: the critical adiabatic index in the presence of a solid core
• Inflated Eccentric Migration of evolving gas giants II: Numerical methodology and basic concepts