Periodic Reporting for period 1 - Magik Star (MAGnetic fIeld and Kinematic coupling for massive STAR formation)
Período documentado: 2019-09-02 hasta 2021-09-01
More importantly, we manage to set up a procedure permitting comparing directly numerical simulation outputs with observations. This was compulsory for the success of the Magik-Star project, and of paramount importance to compare numerical simulations and observations in a broader context. As planned, we studied the interplay of magnetic field and gas dynamic in the context of high-mass star formation in both observations and numerical simulations. We did not find any coupling between the kinematics and the magnetic fields from one parsec to a tenth of a parsec, which is puzzling for the field. This result, if confirmed, will impact strongly our community.
Another item of the Magik-Star project was to question the robustness of the size of cores. We found that the size of the cores — and their mean mass — were strongly affected by the angular resolution. This work was published in 2021 in Astronomy & Astrophysics, and presented in various conferences.
In a sense, more than progressing beyond the state of art, the Magik-Star project questioned and partially rewrote this state to the art. One may see that as a drawback, but we see it as a huge progress. There is nothing more damageable than continuing to build a wall when the very foundation is unstable. Instead, we deconstructed the wall and established new foundations on which we can safely, we hope, re-build our knowledge.
In detail, the Magik-Star project permitted to firmly established that the `cores’ colleagues (and myself!) described as fixed objects with a given size and a given mass are biased by observations. Of course, these cores exist. But their size and flux depend strongly on the angular resolution at which one makes the measure. This result alone impact the community in several ways: i) it is impossible to compare two cores, or two set of cores, if the data have not been acquired with similar physical resolution (the angular resolution expressed in astronomical units at the distance of the target). This is why an incoming publication by the consortium of the ALMA-IMF large program (60 people from 15 countries) decided to smooth their sample to have the same physical scale on target. The Magik-Star project permitted this change of paradigm in the community. ii) The use of `deconvolution’ to account for the beam spreading of the source is inadequate. iii) The peak of the initial function of cores — a paramount indicator to understand the origin of the initial mass function of stars (the so-called IMF) — is very likely inaccurate in all past studies. This aspect is critical and will impact galactic and extra-galactic communities for years.
The Magik-Star project permitted us to establish that previous measurements of the width of filaments were biased by the observational angular resolution. Filamentary structures have been known for more than 50 years but appeared universal in molecular clouds thanks to the observations with the Herschel far-IR satellite around 2010. Since most of the protostars form on the crest of these filaments, they started to play a central role to explain star-formation. Here, several teams used Herschel data and showed that the width of filaments seemed universal at ≈0.1 pc. Theorists tried and explained this typical width from then. More importantly, many observational experiments have been prepared, or proposed, to investigate this width. Magik-Star showed that there is no typical width for filaments, neither in numerical simulations that include all the known physics (including the non-ideal MHD effects) nor in the observations. Or, if a typical width exists in observations, it must be at lower scales than 0.1 pc. Indeed, we observe a linear dependence of the width of the filaments on angular resolution with no sign of convergence in up to date observations.
These results started to diffuse in the community, and we are confident they will close dead ends and open new paths toward a more robust understanding of star-formation.