Breaking the centrifugal barrier to giant planet contraction by magnetic disc braking

Abstract

During the runaway phase of their formation, gas giants fill their gravitational spheres of influence out to Bondi or Hill radii. When runaway ends, planets shrink several orders of magnitude in radius until they are comparable in size to present-day Jupiter; in 1D models, the contraction occurs on the Kelvin-Helmholtz time-scale $t_{\mathrm{KH}}$, which is initially a few thousand years. However, if angular momentum is conserved, contraction cannot complete, as planets are inevitably spun up to their breakup periods $P_{\mathrm{break}}$. We consider how a circumplanetary disc (CPD) can de-spin a primordially magnetized gas giant and remove the centrifugal barrier, provided the disc is hot enough to couple to the magnetic field, a condition that is easier to satisfy at later times. By inferring the planet's magnetic field from its convective cooling luminosity, we show that magnetic spin-down times are shorter than contraction times throughout post-runaway contraction: $t_{\mathrm{mag}}/t_{\mathrm{KH}}\sim (P_{\mathrm{break}}/t_{\mathrm{KH}}{)}^{1/21}\lesssim 1$. Planets can spin down until they corotate with the CPD's magnetospheric truncation radius, at a period $P_{\max }/P_{\mathrm{break}}\sim (t_{\mathrm{KH}}/P_{\mathrm{break}}{)}^{1/7}$. By the time the disc disperses, $P_{\max }/P_{\mathrm{break}}\sim 20-30$; further contraction at fixed angular momentum can spin planets back up to $\sim$$10P_{\mathrm{break}}$, potentially explaining observed rotation periods of giant planets and brown dwarfs.

Accepted to MNRAS Letters

References in corpus (12)

• Two accreting protoplanets around the young star PDS 70
• Models of the in situ formation of detected extrasolar giant planets
• Dead Zone Accretion Flows in Protostellar Disks
• Characterization of exoplanets from their formation III: The statistics of planetary luminosities
• Short dissipation times of proto-planetary discs - an artifact of selection effects?
• Estimating the magnetic field strength in hot Jupiters
• Magnetocentrifugally Driven Flows from Young Stars and Disks. VI. Accretion with a Multipole Stellar Field
• The Boundary between Gas-rich and Gas-poor Planets
• A Systematic Study of the Final Masses of Gas Giant Planets
• The End of Runaway: How Gap Opening Limits the Final Masses of Gas Giants
• The Endgame of Gas Giant Formation: Accretion Luminosity and Contraction Post-Runaway
• The Rotation-Disk Connection in Young Brown Dwarfs: Strong Evidence for Early Rotational Braking

Cited by in corpus (21)

• Formation of Giant Planet Satellites
• Detection and Bulk Properties of the HR 8799 Planets with High Resolution Spectroscopy
• Obliquity Constraints on an Extrasolar Planetary-Mass Companion
• As the Worlds Turn: Constraining Spin Evolution in the Planetary-Mass Regime
• Accreting protoplanets: Spectral signatures and magnitude of gas and dust extinction at H alpha
• Heavy-metal Jupiters by major mergers: metallicity vs. mass for giant planets
• The ESO SupJup Survey III: Confirmation of 13CO in YSES 1 b and Atmospheric Detection of YSES 1 c with CRIRES+
• Spin Evolution of Stellar-mass Black Holes Embedded in AGN disks: Orbital Eccentricity Produces Retrograde Circumstellar Flows
• Planetary Spin and Obliquity from Mergers
• Primordial Obliquities of Brown Dwarfs and Super-Jupiters from Fragmenting Gravito-Turbulent Discs
• Boundary Layer Circumplanetary Accretion: How Fast Could an Unmagnetized Planet Spin Up Through Its Disk?
• Prograde and Retrograde Gas Flow around Disk-embedded Companions: Dependence on Eccentricity, Mass and Disk Properties
• Rotation and Abundances of the Benchmark Brown Dwarf HD 33632 Ab from Keck/KPIC High-resolution Spectroscopy
• Atmospheric characterization of the super-Jupiter HIP 99770 b with KPIC
• On the Terminal Spins of Accreting Stars and Planets: Boundary Layers
• Detecting Planetary Oblateness in the Era of JWST: A Case Study of Kepler-167e
• Magnetic Fields and Accreting Giant Planets around PDS 70
• Warm Jupiters Beyond the Tidal Synchronization Limit May Exhibit a Wide Range of Secondary Eclipse Depths
• Distinct Rotational Evolution of Giant Planets and Brown Dwarf Companions
• The Critical Core Mass of Rotating Planets
• In situ formation of super-Earth/sub-Neptune driven by the planetary rotation