Periodic Reporting for period 4 - UFOS (Unveiling Planet Formation by Observations and Simulations)
Reporting period: 2022-12-01 to 2023-05-31
The UFOS project aims to unveil planet formation using state-of-the-art simulations and observations. We want to understand the gas and dust dynamics and evolution in protoplanetary disks. Where are the pebbles concentrated in disks? Where can planets form? What is the influence of the dust on the gas and vice versa? We want to address these questions with UFOS using state-of-the-art theoretical models. These models allow us to solve for the hydrodynamical and magneto-hydrodynamical equations for a full global disk model. The results show us the detailed dynamics of the gas, similar to that of our solar system 4.5 billion years ago. Understanding how the planets are formed is one of the biggest questions in modern astrophysics.
More specifically, the question that needs to be addressed is the level of gas turbulence in protoplanetary disks. The gas turbulence controls the transport of angular momentum and so the evolution of the disk. Another immediate goal of our project is the evolution of the dust component. How do larger dust grains evolve in the disk? Where do they concentrate and form the first proto-planets?
More specifically, the question that needs to be addressed is the level of gas turbulence in protoplanetary disks. The gas turbulence controls the transport of angular momentum and so the evolution of the disk. Another immediate goal of our project is the evolution of the dust component. How do larger dust grains evolve in the disk? Where do they concentrate and form the first proto-planets?
We have worked and published many results ranging from the hot innermost regions of protoplanetary disks to the cold outer disk regions. We have investigated the conditions for planet formation at the dust sublimation zone. Dust grains, which grow in the disk, drift to the inner disk regions where they get trapped due to a pressure maximum. Our results show a robust pressure maximum due to the transition of accretion stress caused by the ionization transition. Here the magneto-rotational instability is getting damped which leads to a rise in the surface density. Our results also show that only under certain conditions we expect the grains to get trapped at the inner rim. In case the turbulence is too high we found that the grains do not grow that fast and can pass through the pressure trap. We also found that young forming proto-planets can get trapped at the inner rim which could lead to the potential formation of a chain of super-Earth, similar as it was found for the Trappist-1 system. We have also worked on the gas and dust dynamics in the so called dead-zone. Here we expect hydrodynamical instabilities to dominate. With our works we have investigated the strength of the vertical shear instability (VSI). We found that the instability can efficiently mix up the grains in the disk. We also found in high-resolution simulations that the gas becomes turbulent in between the large scale motions of the vertical shear instability. Further we have found that there is also a accretion stress transition zone for the VSI which causes the pebble drift to slow done. This could also generate gaps and rings, which are currently observed with radio interferometer telescopes. We have developed a new dust method to solve for the individual motions of dust pebbles. We are also collaborating with several other teams to understand for the scattered light and dust continuum observations of several protoplanetary disks.
With the new dust module we have investigated the streaming instability for the first time in global simulations. Large dust pebbbles concentrate at the disk midplane and they locally dominate the mass content, which leads to a dust drag force back onto the gas. This drag gives rise to a new class of instabilities for which the streaming instability is a well-known candidate. In our results, we show that the streaming instability reaches a steady state in a case of inward drifting pebbles and a low level of turbulence.
Further our results for the first time combine the kinematics derived from 3D global hydrodynamical simulations of the vertical shear instability with line observations by the Atacama Large Millimeter Array. For that we post-processed the data with the radiative transfer code RADMC3D, we calculate the expect line emission for 12CO line emission. Using a model we could then subtract the Keplerian velocity from the observed line emission, estimating the emission surface and calculating the velocity profile at the emission surface. What remains is the residual map of the blue or red shifted line center, which corresponds directly to the velocity deviations. The results show for the first time that VSI turbulence can be observed with ALMA (Barraza et al. 2021).
In a follow-up work (Barraza 2023) we used the same framework to investigate for models with embedded planets. In this case, the planet can perturb the disk in addition to the vertical shear instability. The work showed that only very massive planets, like Jupiter mass planet produce perturbations in the velocity which can clearly be detected. Saturn mass planets on the other hand are more difficult to detect due to the interplay between VSI and the planet.
In another key work series (Delage et al. 2022,2023) we describe the disk evolution under a coupled framework of non-ideal MHD, viscous evolution by the magneto-rotational instability and non-ideal MHD terms coupled to the dust evolution. For the first time we can investigate for the formation of dust rings by the variations of the MHD efficiency in the protoplanetary disks. The results show a clear formation of rings in the regions between 10 to 100 au due to the dead-zone outer edge and the effect of dust grow. Small grains capture efficiently free electrons and so reduce the MRI activity while a depletion of grains favours for MRI turbulence.
With the new dust module we have investigated the streaming instability for the first time in global simulations. Large dust pebbbles concentrate at the disk midplane and they locally dominate the mass content, which leads to a dust drag force back onto the gas. This drag gives rise to a new class of instabilities for which the streaming instability is a well-known candidate. In our results, we show that the streaming instability reaches a steady state in a case of inward drifting pebbles and a low level of turbulence.
Further our results for the first time combine the kinematics derived from 3D global hydrodynamical simulations of the vertical shear instability with line observations by the Atacama Large Millimeter Array. For that we post-processed the data with the radiative transfer code RADMC3D, we calculate the expect line emission for 12CO line emission. Using a model we could then subtract the Keplerian velocity from the observed line emission, estimating the emission surface and calculating the velocity profile at the emission surface. What remains is the residual map of the blue or red shifted line center, which corresponds directly to the velocity deviations. The results show for the first time that VSI turbulence can be observed with ALMA (Barraza et al. 2021).
In a follow-up work (Barraza 2023) we used the same framework to investigate for models with embedded planets. In this case, the planet can perturb the disk in addition to the vertical shear instability. The work showed that only very massive planets, like Jupiter mass planet produce perturbations in the velocity which can clearly be detected. Saturn mass planets on the other hand are more difficult to detect due to the interplay between VSI and the planet.
In another key work series (Delage et al. 2022,2023) we describe the disk evolution under a coupled framework of non-ideal MHD, viscous evolution by the magneto-rotational instability and non-ideal MHD terms coupled to the dust evolution. For the first time we can investigate for the formation of dust rings by the variations of the MHD efficiency in the protoplanetary disks. The results show a clear formation of rings in the regions between 10 to 100 au due to the dead-zone outer edge and the effect of dust grow. Small grains capture efficiently free electrons and so reduce the MRI activity while a depletion of grains favours for MRI turbulence.
We have also made progress beyond what we expected. This includes the characterisation of dust grains, their properties to absorb and scatter radiation. Our result showed that the detailed shape of the grains is very important for the efficiency to scatter and polarise the radiation. Recent state-of-the-art observations showed the dust continuum radiation is polarised which could be caused either by the intrinsic alignment of magnetic fields or by self-scattering. For both processes the detailed characteristics how grains absorb, scattered and change the polarisation vector is of highest importance, even more when the grains are porous. Especially when grains are small we do not expect that the grains are very compact objects.
Another project which was beyond the expected project was that we got access to observation of several protoplanetary disks with the MUSE instrument at the VLT. In the work (Flores et al. 2023) we observed for the first time disk driven magnetic winds and jets. In this work we investigated the inclination and position angle of the fast outflows and could relate them to the dust emission in the outer disk regions. This was a pioneer work showing for the first time the kinematics of spatial resolved disk winds.
Another project which was beyond the expected project was that we got access to observation of several protoplanetary disks with the MUSE instrument at the VLT. In the work (Flores et al. 2023) we observed for the first time disk driven magnetic winds and jets. In this work we investigated the inclination and position angle of the fast outflows and could relate them to the dust emission in the outer disk regions. This was a pioneer work showing for the first time the kinematics of spatial resolved disk winds.