Introduction
Protoplanetary disks are structures of gas and dust that orbit newly formed stars, providing the raw material from which planets assemble. Spanning up to hundreds of astronomical units, these disks evolve over millions of years through accretion, dispersal, and the growth of solid bodies. Understanding their structure and evolution is central to explaining the origins of the Solar System and the thousands of exoplanetary systems discovered around other stars.
- Form around protostars and persist for ~1–10 million years
- Contain the gas, dust, and ice from which all planetary bodies ultimately originate
- Observed across a wide range of stellar masses with instruments such as ALMA and the VLA
- Link stellar formation to planetary system architectures
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Evolution
Over multi-million-year lifetimes, protoplanetary disks lose mass through accretion onto the central star, photoevaporation driven by stellar and external radiation, and the gradual incorporation of material into planetary bodies. The interplay of these processes sets the stage for each subsequent phase of planet formation and ultimately determines the mass and composition budget available to nascent planets.
- Disk masses and lifetimes are constrained by infrared and millimeter surveys of star-forming regions
- Turbulent spreading and wind-driven mass loss redistribute angular momentum over time
- Stellar irradiation creates temperature gradients that drive thermally driven disk winds
- Disk dissipation timescales vary with stellar mass, multiplicity, and environment
Learn more:
- Accretion
- Thermodynamic Structure
- Magnetically Driven Turbulence in the Inner Regions of Protoplanetary Disks — Rea et al. (2024)
- High-resolution Simulation of Protoplanetary Disk Turbulence Driven by the Vertical Shear Instability — Shariff & Umurhan (2024)
Accretion
Gas and solids spiral inward through the disk via angular momentum transport, feeding material onto the central star and setting disk lifetimes. Magnetically driven turbulence, laminar magnetic torques, and disk winds are key candidates for sustaining the accretion rates inferred from observations of young stellar objects. Our group investigates these mechanisms using high-fidelity magnetohydrodynamic simulations.
- Accretion rates in T Tauri disks are typically ~10⁻⁸ solar masses per year
- The magnetorotational instability (MRI) is a leading driver of turbulent angular momentum transport
- Non-ideal MHD effects (Ohmic diffusion, ambipolar diffusion, Hall effect) regulate MRI activity
- Magnetically driven disk winds may dominate angular momentum transport in weakly ionized regions
Learn more:
- Magnetohydrodynamics
- Magnetorotational Instability
- Magnetically Driven Turbulence in the Inner Regions of Protoplanetary Disks — Rea et al. (2024)
- Jacob B. Simon — expert in magnetically driven accretion processes
Thermodynamic Structure
The temperature and density structure of a protoplanetary disk is set by the balance between stellar irradiation, turbulent heating, and radiative cooling. Radial and vertical gradients in these quantities influence gas and dust dynamics, the location of condensation fronts (“snowlines”), and the character of disk instabilities. Accurately modeling this structure is essential for making realistic comparisons with infrared and millimeter-wave observations.
- Midplane temperatures range from ~1500 K near the star to ~10 K in the outer disk
- Snowlines (e.g., the water ice line) mark transitions in dust composition and influence solid mass budgets
- Disk flaring allows stellar irradiation to heat the disk surface at large radii
- Turbulent diffusion couples the thermal and chemical evolution of disk material
Learn more:
- Radiation Hydrodynamics
- Vertical Shear Instability
- Length and Velocity Scales in Protoplanetary Disk Turbulence — Sengupta et al. (2024)
- Turbulence in Particle-laden Midplane Layers of Planet-forming Disks — Sengupta & Umurhan (2023)
Vortices
Large-scale anticyclonic vortices can form in protoplanetary disks through the Rossby wave instability and other mechanisms, persisting for hundreds to thousands of orbital periods. These structures efficiently concentrate dust particles, potentially triggering rapid planetesimal and protoplanet formation, and may leave observable imprints as the asymmetric dust rings detected by ALMA.
- Vortices form at pressure bumps such as the edges of dead zones or gaps opened by planets
- Dust-to-gas ratios inside vortices can greatly exceed disk-average values, aiding gravitational collapse
- 3D simulations with self-gravity show that vortices can produce protoplanets on surprisingly short timescales
- Vortex formation has been proposed as a pathway to rapid planet formation
Learn more:
- Rossby Wave Instability
- Rapid Protoplanet Formation in Vortices: Three-dimensional Local Simulations with Self-gravity — Lyra et al. (2024)
- On the Origin of Dust Structures in Protoplanetary Disks: Constraints from the Rossby Wave Instability — Chang et al. (2023)
- Planets and planetesimals at cosmic dawn: vortices as planetary nurseries — Eriksson et al. (2025)