Periodic Reporting for period 5 - new-ppd-environments (First-principles global MHD disc simulations: Defining planet-forming environments in early solar systems)
Período documentado: 2020-06-01 hasta 2021-05-31
Planets have fascinated professional astronomers as well as casual stargazers for centuries. Since ancient times, we have literally only known a handful of planets, all orbiting our own star, the Sun. However, during the last two decades, and with the help of small ground-based telescopes and enormous space missions like Kepler and CoRoT alike, astronomers have discovered thousands of so-called exoplanets orbiting distant stars in our neighbourhood of the Milky Way.
In their role as planet nurseries, protoplanetary discs are of key interest to planet formation theory. Their dynamical, radiative and thermodynamic properties critically define the environment for embedded solids: dust grains, pebbles and planetesimals. In short, the building blocks of planet formation. The discs' dynamics and structure in turn depend critically on the influence of magnetic fields that couple to tenuously ionised and low-density regions. Being comparatively cold and dense, the ionisation state of the disc plasma is dominated by external far-UV, X-Ray, and cosmic-ray radiation, leading to a layered vertical structure - with turbulent, magnetised surface layers and a magnetically-decoupled midplane. This classic dead-zone picture is now turned upside-down by previously ignored micro-physical effects.
The aim of my research project was to create the most realistic radiation-MHD computer simulations of protoplanetary discs of gas and dust, thus defining the environment that shapes the early development of planetary systems. With the final steps, that is, the inclusion of radiative processes as well as a representative thermochemistry, the ERC project has produced the new reference standard in the field. We moreover laid the groundwork for exploiting our models via synthetic observations, producing templates of spectral line profiles that will lead the way in interpreting current and future observations of T Tauri disk winds in nearby star-forming regions.
In their role as planet nurseries, protoplanetary discs are of key interest to planet formation theory. Their dynamical, radiative and thermodynamic properties critically define the environment for embedded solids: dust grains, pebbles and planetesimals. In short, the building blocks of planet formation. The discs' dynamics and structure in turn depend critically on the influence of magnetic fields that couple to tenuously ionised and low-density regions. Being comparatively cold and dense, the ionisation state of the disc plasma is dominated by external far-UV, X-Ray, and cosmic-ray radiation, leading to a layered vertical structure - with turbulent, magnetised surface layers and a magnetically-decoupled midplane. This classic dead-zone picture is now turned upside-down by previously ignored micro-physical effects.
The aim of my research project was to create the most realistic radiation-MHD computer simulations of protoplanetary discs of gas and dust, thus defining the environment that shapes the early development of planetary systems. With the final steps, that is, the inclusion of radiative processes as well as a representative thermochemistry, the ERC project has produced the new reference standard in the field. We moreover laid the groundwork for exploiting our models via synthetic observations, producing templates of spectral line profiles that will lead the way in interpreting current and future observations of T Tauri disk winds in nearby star-forming regions.
In an effort led by senior team-member Ch. Brinch, we have obtained Atacama Large (sub-)Millimeter Array (ALMA) data of the binary protostars IRS-43. The ALMA data in the sub-mm band has been thoroughly analysed with respect to the highly unusual mutual misalignment of the circumbinary disk with the two circumstellar disks. The case study resulted in a high-profile publication in Astrophysical Journal Letters (Brinch et al. 2016, ApJ Letters), with widely received press-releases, spawned in media outlets across the globe (among others: Nature news, Sky & Telescope, New Scientist, Popular Mechanics, IFL Science, space.com as well as roughly one hundred independent newspapers around the globe).
Imaging of dust continuum emitted from disks around nearby protostars reveals diverse substructure. Turbulence in the realm of non-ideal magnetohydrodynamics is one candidate for explaining the generation of zonal flows which can lead to local dust enhancements. In our effort, we consider combinations of vertical and azimuthal initial net flux and perform 3D non-ideal MHD simulations aimed at studying self-organization induced by the Hall effect in turbulent disks. We include dust grains, treated in the fluid approximation, in order to study their evolution subject to the emerging zonal flows. In the regime of a dominant Hall effect, we robustly obtain large-scale organized concentrations in the vertical field that remain stable for many orbits (Krapp et al. 2018, ApJ). Our research has, moreover, found that including a moderately strong net-azimuthal magnetic flux can significantly alter the dynamics, partially preventing the self-organization of zonal flows.
Outflows driven by large-scale magnetic fields likely play an important role in the evolution and dispersal of protoplanetary disks, and in setting the conditions for planet formation. We extend our 2D axisymmetric non-ideal MHD model of these outflows by incorporating radiative transfer and simplified thermochemistry, with the twin aims of exploring how heating influences wind launching, and illustrating how such models can be tested through observations of diagnostic spectral lines. Our model disks launch magnetocentrifugal outflows primarily through magnetic tension forces, so the mass-loss rate increases only moderately when thermochemical effects are switched on. For typical field strengths, thermochemical and irradiation heating are more important than magnetic dissipation. We furthermore find that the entrained vertical magnetic flux diffuses out of the disk on secular timescales as a result of non-ideal MHD. Through post-processing line radiative transfer, we demonstrate that spectral line intensities and moment-1 maps of atomic oxygen, the HCN molecule, and other species show potentially observable differences between a model with a magnetically driven outflow and one with a weaker, photoevaporative outflow (Gressel et al. 2020, ApJ).
Imaging of dust continuum emitted from disks around nearby protostars reveals diverse substructure. Turbulence in the realm of non-ideal magnetohydrodynamics is one candidate for explaining the generation of zonal flows which can lead to local dust enhancements. In our effort, we consider combinations of vertical and azimuthal initial net flux and perform 3D non-ideal MHD simulations aimed at studying self-organization induced by the Hall effect in turbulent disks. We include dust grains, treated in the fluid approximation, in order to study their evolution subject to the emerging zonal flows. In the regime of a dominant Hall effect, we robustly obtain large-scale organized concentrations in the vertical field that remain stable for many orbits (Krapp et al. 2018, ApJ). Our research has, moreover, found that including a moderately strong net-azimuthal magnetic flux can significantly alter the dynamics, partially preventing the self-organization of zonal flows.
Outflows driven by large-scale magnetic fields likely play an important role in the evolution and dispersal of protoplanetary disks, and in setting the conditions for planet formation. We extend our 2D axisymmetric non-ideal MHD model of these outflows by incorporating radiative transfer and simplified thermochemistry, with the twin aims of exploring how heating influences wind launching, and illustrating how such models can be tested through observations of diagnostic spectral lines. Our model disks launch magnetocentrifugal outflows primarily through magnetic tension forces, so the mass-loss rate increases only moderately when thermochemical effects are switched on. For typical field strengths, thermochemical and irradiation heating are more important than magnetic dissipation. We furthermore find that the entrained vertical magnetic flux diffuses out of the disk on secular timescales as a result of non-ideal MHD. Through post-processing line radiative transfer, we demonstrate that spectral line intensities and moment-1 maps of atomic oxygen, the HCN molecule, and other species show potentially observable differences between a model with a magnetically driven outflow and one with a weaker, photoevaporative outflow (Gressel et al. 2020, ApJ).
The inclusion of simplified radiation physics into the NIRVANA MHD code (Gressel 2017, JoP CS) has further increased the realism of our magneto-thermal wind launching simulations, and will help to understand its effect on disk evolution in a quantitative manner. We have furthermore implemented drag-force-coupled dust fluids, which are used to study the evolution of small dust up to mm-sized grains, whose mutual distribution with the gas is crucial in interpreting (sub-)mm dust-continuum emission and establish an understanding of the most important physical effects at play in shaping planet-forming disks. To establish the foundation for one of the key aims of the ERC project, the study of full non-ideal MHD (Ohmic resistivity, ambipolar diffusion and the Hall effect), our team has implemented the missing third non-ideal effect, i.e. the Hall effect, into our framework (Krapp et al. 2018, ApJ). We have further modified the NIRVANA code to support a complex thermodynamic equation of state, including the dissociation and ionisation of Hydrogen-Helium mixtures, important calorimetric effects that will determine the temperature structure of strongly heated gas (e.g. gas falling onto an embedded proto-planet). In their entirety, the set of implemented features will allow us to compete at international level in the forthcoming years.
Our research team has championed a multi-faceted approach of performing numerical simulations of diverse complex aspects of protoplanetary systems. Each of the individual studies has implemented key technologies for tackling novel conceptual, numerical or computational challenges. This concerted effort has led to a number of surprising and thought-provoking results, which each challenge conventional wisdom about these systems. The ERC action has accordingly led to several high-impact publications, notably an observational study of the binary system IRS43, published in ApJ Letters (which moreover received a sizable press coverage around the globe); a computational study of a novel planet-migration torque (Benítez-Llambay & Pessah 2018, ApJ Letters) based on the scattering of pebbles; as well as, a linear stability analysis of the important streaming instability for the novel case of particle-size distributions (Krapp et al. 2019, ApJ Letters). The work on the core subject of the ERC project, that is, magneto-centrifugally launched and thermally-assisted disk outflows, has led to a comprehensive publication (Gressel et al. 2020, ApJ), which promises to provide a new reference standard for the field.
Our research team has championed a multi-faceted approach of performing numerical simulations of diverse complex aspects of protoplanetary systems. Each of the individual studies has implemented key technologies for tackling novel conceptual, numerical or computational challenges. This concerted effort has led to a number of surprising and thought-provoking results, which each challenge conventional wisdom about these systems. The ERC action has accordingly led to several high-impact publications, notably an observational study of the binary system IRS43, published in ApJ Letters (which moreover received a sizable press coverage around the globe); a computational study of a novel planet-migration torque (Benítez-Llambay & Pessah 2018, ApJ Letters) based on the scattering of pebbles; as well as, a linear stability analysis of the important streaming instability for the novel case of particle-size distributions (Krapp et al. 2019, ApJ Letters). The work on the core subject of the ERC project, that is, magneto-centrifugally launched and thermally-assisted disk outflows, has led to a comprehensive publication (Gressel et al. 2020, ApJ), which promises to provide a new reference standard for the field.