Periodic Reporting for period 4 - MagneticYSOs (Interpreting Dust Polarization Maps to Characterize the Role of the Magnetic Field in Star Formation Processes)
Reporting period: 2021-01-01 to 2022-06-30
The MagneticYSOs project has adressed the modern challenges in our quest to build a complete understanding of star and planet formation.
More specifically, we investigated how to probe magnetic fields and studied their role in building the stars and planets that populate our Galaxy.
The interstellar medium, where stars are born, is permeated by large-scale magnetic fields. These magnetic fields were suggested to have a crucial role in supporting the high density gas against its own gravity, that ultimately triggers the formation of low mass stars as our own Sun.
Star formation models also suggested that these magnetic fields could also significantly affect the motions in the star-forming cores, ultimately being key to rule the formation of the youngest protoplanetary disks, and thus the initial conditions leading to the formation of planets in these disks.
Unfortunately the magnetic field cannot be observed directly. In the presence of a magnetic field, however, theories predict that the dust grains contained in an astrophysical medium see their long axes partially align perpendicularly to the magnetic field lines. Their radiation is then emitted in a preferred direction and the light emitted is then called "polarized". It is this polarized light which is widely used by the atrsonomical community to trace magnetic fields in star-forming cores.
However, wether such observations do produce robust constraints on the topology of magnetic fields, and wether they can be used to study the role of magnetic fields while stars and planets form, remained very scarcely tested.
Thanks to the novel approaches of MagneticYSOs, combining a detailed analysis of complete set of observational constraints and their confrontation to comprehensive magnetized models of protostellar collapse, we aimed at putting unprecedented constraints on the methods to measure magnetic fields and shed light on their role in forming stars and protoplanetary disks.
More specifically, we investigated how to probe magnetic fields and studied their role in building the stars and planets that populate our Galaxy.
The interstellar medium, where stars are born, is permeated by large-scale magnetic fields. These magnetic fields were suggested to have a crucial role in supporting the high density gas against its own gravity, that ultimately triggers the formation of low mass stars as our own Sun.
Star formation models also suggested that these magnetic fields could also significantly affect the motions in the star-forming cores, ultimately being key to rule the formation of the youngest protoplanetary disks, and thus the initial conditions leading to the formation of planets in these disks.
Unfortunately the magnetic field cannot be observed directly. In the presence of a magnetic field, however, theories predict that the dust grains contained in an astrophysical medium see their long axes partially align perpendicularly to the magnetic field lines. Their radiation is then emitted in a preferred direction and the light emitted is then called "polarized". It is this polarized light which is widely used by the atrsonomical community to trace magnetic fields in star-forming cores.
However, wether such observations do produce robust constraints on the topology of magnetic fields, and wether they can be used to study the role of magnetic fields while stars and planets form, remained very scarcely tested.
Thanks to the novel approaches of MagneticYSOs, combining a detailed analysis of complete set of observational constraints and their confrontation to comprehensive magnetized models of protostellar collapse, we aimed at putting unprecedented constraints on the methods to measure magnetic fields and shed light on their role in forming stars and protoplanetary disks.
By exploring a sample of 16 of the youngest protostars in our Galaxy, thanks to the interferometric array of the Institute of Millimeter Radio Astronomy (IRAM), we have shown that a majority of disks where planets will be formed are born much smaller than expected (Maury et al. 2019). We have suggested that the size of these disks around young protostars, currently being formed, are in agreement with predictions of models where the magnetic field plays a key role, and suggested that the influence of the magnetic field had been so far been underestimated.
The MagneticYSOs team then has analyzed observations of the polarized light from dust grains for 12 of the youngest protostars in the Solar neighborhood, and shown that all these progenitors of solar-type stars show a rather high fraction of aligned dust grains, which suggest they are magnetized to some levels. We have also tackled the question from the thoretical point of view, coupling dust alignment models to state-of-the-art magneto-hydrodynamical models of star formation to show that magnetic fields in star-forming cores can be accurately traced by the emission of aligned dust, and have characterized the dust grain alignment efficiency in protostellar environments.
Moreover, we have also been able to show for the first time that the magnetic field plays a fundamental role in the collapse of protostars and formation of protostellar disks, as our observations and their confrontation to models suggest they efficiently brake the material during the formation of a star and its disk.
We have explored the influence of local conditions to set the efficiency of the braking, such as the gas ionization and the dust grains sizes, and have found unexpected conditions, such as the existence of very large grains and an ionization of the gas at small scales one order of magnitude larger than the fiducial values used in most works.
These are key to couple the magnetic fields to the circumstellar material, so our results call for a revision of the conditions used in the star formation models in the future.
Thanks to our concerted effort, we have been able to propose a refined scenario to solve the long-standing angular momentum problem, where magnetic fields, angular momentum and local properties of the gas and dust in embedded protostars combine to regulate the growth of the star and its surrounding disk.
The MagneticYSOs team then has analyzed observations of the polarized light from dust grains for 12 of the youngest protostars in the Solar neighborhood, and shown that all these progenitors of solar-type stars show a rather high fraction of aligned dust grains, which suggest they are magnetized to some levels. We have also tackled the question from the thoretical point of view, coupling dust alignment models to state-of-the-art magneto-hydrodynamical models of star formation to show that magnetic fields in star-forming cores can be accurately traced by the emission of aligned dust, and have characterized the dust grain alignment efficiency in protostellar environments.
Moreover, we have also been able to show for the first time that the magnetic field plays a fundamental role in the collapse of protostars and formation of protostellar disks, as our observations and their confrontation to models suggest they efficiently brake the material during the formation of a star and its disk.
We have explored the influence of local conditions to set the efficiency of the braking, such as the gas ionization and the dust grains sizes, and have found unexpected conditions, such as the existence of very large grains and an ionization of the gas at small scales one order of magnitude larger than the fiducial values used in most works.
These are key to couple the magnetic fields to the circumstellar material, so our results call for a revision of the conditions used in the star formation models in the future.
Thanks to our concerted effort, we have been able to propose a refined scenario to solve the long-standing angular momentum problem, where magnetic fields, angular momentum and local properties of the gas and dust in embedded protostars combine to regulate the growth of the star and its surrounding disk.
Our work has globally highlighted the cornerstone role of the magnetic field during the early phases of the star and disk formation, thanks to an unprecedented combination of observational data and physical models of the protostellar collapse.
We have been able to robustely prove that dust polarized emission is a good tracer of magnetic field structure in the conditions typical of young protostars, and that the properties of stars and their disks are largely influenced by magnetic fields being able to couple more or less efficiently depending on the local gas ionization and dust properties.
We have been able to robustely prove that dust polarized emission is a good tracer of magnetic field structure in the conditions typical of young protostars, and that the properties of stars and their disks are largely influenced by magnetic fields being able to couple more or less efficiently depending on the local gas ionization and dust properties.