Dottorato - PhD thesis
Area Tematica: RSN 2: Stelle, popolazioni stellari e mezzo interstellare - RSN3: Sole e Sistema Solare - RSN 5: Tecnologie avanzate e strumentazione
Referente: Stavro L. Ivanovski (
Titolo: Dust Dynamics in Protoplanetary Disks: The Influence of both Non-Spherical Convex and Fractal Particles on Pebble Accretion
Decorrenza: 18.05.2025
The dynamics of dust particles in protoplanetary disks, from sub-micron grains to meter-sized bodies, is governed by the interaction between gas and the gravitational field of the central star. For subsonic motion, the gas exerts a drag force on the dust particles, causing acceleration or deceleration. When the mean free path of gas molecules is much larger than the particle size, the particles move in the Epstein regime, where drag is due to molecular collisions. When the particle size is comparable to the mean free path, the particles are in the Stokes regime, where drag is governed by viscous flow around the particle.In the Stokes regime, particles with different shapes, sizes, or compositions can be described using the dimensionless stopping time, or Stokes number. Particles with the same Stokes number behave similarly. In the Epstein regime, however, particle shape, size, and composition significantly affect their aerodynamics and motion.
Building on previous work modeling non-spherical dust in rarefied gas environments (Ivanovski et al. 2017a, 2017b), we will study the dynamics of such particles in protoplanetary disks using the NSP-PRED((Non-Spherical Dust Model for Protoplanetary Rarefied Environments of Dust) code (Ivanovski eta al. 2021, EPSC). This model simulates dust motion in the Epstein regime, where particle shape significantly affects terminal velocity even at equal mass and density. A key application is the analysis of second-generation dust in disks like HD163296 (Turrini et al. 2021), where high-velocity impacts from embedded giant planets generate vertically distributed dust and trigger ice sublimation, releasing gas species such as H₂O in low-density regions where Epstein drag dominates.
The NSP-PRED model will be used to simulate the dynamics of this dust and to constrain the dust size distribution in vertical regions and disk gaps. These simulations will be supported by ALMA observations and laboratory measurements of non-spherical particles.
A second goal of the project is to study how non-sphericity and particle rotation affect radial drift and vertical settling. For this purpose, we have developed an upgraded version of the PHANTOM code, called PHANTOM-NSP. This is a 3D+t SPH and MHD code that includes modules for self-gravity, dust-gas mixtures, viscosity, and photo-evaporation. We have implemented ellipsoidal particles and averaged drag coefficients for non-spherical shapes. The code has been used to simulate vertical settling of spherical and non-spherical dust, showing that larger spherical particles settle faster and that settling is slower in denser gas disks.
Observations of protoplanetary disks show a variety of substructures such as rings, gaps, spirals, and asymmetries. These features are not yet fully understood. High-resolution observations from instruments like ALMA (Fedele et al. 2017, 2018, Ansdell et al., 2016 and Andrews et al., 2018), VLT, and LBT, as well as future data from the James Webb Space Telescope, will provide new insights into disk structure and planet formation. In particular, edge-on disks allow direct observation of vertical dust distribution, which is key to studying dust settling. Radial drift is also a critical process, as it determines the radial extent of the dust disk.
The PhD student will use PHANTOM-NSP to simulate selected protoplanetary disks, varying dust shape, porosity, and density, and using constraints from the NSP-PRED simulations. The goal is to reconstruct the structure of these disks by analyzing vertical settling and radial drift.
The PhD student will be involved in the development and application of the NSP-PRED and PHANTOM-NSP models. The activities will include:
- Simulations of non-spherical dust dynamics in the Epstein regime using NSP-PRED, with application to second-generation dust in disks like HD163296.
- Simulations of vertical settling and radial drift using PHANTOM-NSP, with comparisons between spherical and non-spherical particles.
- Analysis of observational data from ALMA and other telescopes to constrain model parameters and validate simulation results.
The PhD student will develop strong skills in computational astrophysics, dust dynamics, and the analysis of observational data. This research will be conducted within the "Planetary Systems and Origin of Life" group at INAF–Osservatorio Astronomico di Trieste (OATs) (S. Ivanovski, L. Biasiotti, L. Calderone, F. Dogo, S. Monai, P. Simonetti and G. Vladilo) in collaboration with national partners, including the University of Parthenope, Astronomical Observatory Accetri and international teams based in Germany and Sweden.
