Grain growth in proto-planetary discs: the role of scattering
Lead Research Organisation:
University of Cambridge
Department Name: Institute of Astronomy
Abstract
Planet-forming discs are the natural environment in which exoplanets are assembled. According to the core-accretion model, planet formation is a bottom up process: initially m-sized, dust grains grow several orders of magnitude to form roughly 100 km-large planetesimals. This is why assessing whether grain growth is actually taking place in Myr-old protoplanetary discs is critical to understand how the currently observed Gyr-old exoplanets are born. Furthermore, estimates of the maximum grain size in planet-forming discs posit strong constraints on the planet-formation models (e.g., how rapidly do planetesimals form? Which is the minimum amount of solids in discs at a given time for planet formation to be viable?). The grain-growth hypothesis has been tested relying on the spectral index, a (either spatially resolved or, more commonly, disc-integrated). In the optically thin regime and the Rayleigh-Jeans approximation, it can be simply related to the absorption spectral index. The latter, in turn, is a function of the maximum grain size. This was the presence of mm to cm large grains was inferred in the past years. However, it is now known that optically thick sub-structures such as rings or spirals are ubiquitous in protoplanetary discs suggesting that the previous approximation is no longer valid. Indeed, in the optically thick case a = 2 regardless of the grain size. Moreover, recent works focusing on single sources suggest that also dust self-scattering can be important in the optically thin scenario: overlooking scattering brings about an overestimation of the dust sizes for grains with high albedo. In my project I study grain growth in a self-consistent way to assess the role of dust scattering in the determination of the maximum grain size. Confronting models and data, my aim is that of providing reliable estimates of the maximum grain sizes in populations of discs in the nearby star forming regions.
Organisations
People |
ORCID iD |
Cathie Clarke (Primary Supervisor) | |
Francesco Zagaria (Student) |
Publications
Zagaria F
(2023)
Dust dynamics in planet-forming discs in binary systems.
Zagaria F
(2021)
On dust evolution in planet-forming discs in binary systems - I. Theoretical and numerical modelling: radial drift is faster in binary discs
in Monthly Notices of the Royal Astronomical Society
Zagaria F
(2021)
On dust evolution in planet-forming discs in binary systems - II. Comparison with Taurus and ? Ophiuchus (sub-)millimetre observations: discs in binaries have small dust sizes
in Monthly Notices of the Royal Astronomical Society
Zagaria F
(2022)
Modelling the secular evolution of protoplanetary disc dust sizes - a comparison between the viscous and magnetic wind case
in Monthly Notices of the Royal Astronomical Society
Zagaria F
(2023)
Dust dynamics in planet-forming discs in binary systems.
in European physical journal plus
Zagaria F
(2022)
Stellar multiplicity affects the correlation between protoplanetary disc masses and accretion rates: binaries explain high accretors in Upper Sco
in Monthly Notices of the Royal Astronomical Society
Studentship Projects
Project Reference | Relationship | Related To | Start | End | Student Name |
---|---|---|---|---|---|
ST/V50659X/1 | 30/09/2020 | 29/09/2024 | |||
2442694 | Studentship | ST/V50659X/1 | 30/09/2020 | 29/09/2023 | Francesco Zagaria |
Description | My work on discs in binaries shows that dust grains in these systems are removed faster than in single star discs (Zagaria et al., 2021a). These mechanisms can explain the smaller disc sizes previously measured in binary systems and gave predictions on the gas to dust size ratios that were later confirmed (Zagaria et al., 2021b). When studying the accretion properties of discs in binary systems, I noticed that they have higher accretion rates than those around single stars. This can explain why accretion rates can be very high even if discs are old (Zagaria et al., 2022a). These results have been summarised in my EPJP review (Zagaria et al., 2023). Finally, I used my simple models to compare dust sizes evolving in the viscous case and under the effect of MHD winds. This has been an open problem in the field for several years. I showed that the currently available ALMA data cannot distinguish between these two evolutionary pathways and that longer observation times are needed to understand if discs are viscous or not (Zagaria et al., 2022b). All these works have been carried out in close collaboration with researchers here in the UK and abroad (Milan, Munich, Hawai'i). |
Exploitation Route | Some of my analysis is self-conclusive, but for other topics there are large areas of improvement, and I'm already collaborating with other groups of scientists worldwide to address different aspects of my research (e.g., instead of dust can we use other tracers to study disc evolution?). |
Sectors | Education Other |
Description | I've been contributing to outreach activities in my department and my home country, talking about my research on a wider non-academic audience. |