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Accueil > Séminaires & Soutenances > Séminaires, soutenances de thèses et HDR précédents > 2019 > Séminaires 2019 > Le jeudi 6 juin 2019 à 10h30

Le jeudi 6 juin 2019 à 10h30

Lieu : Salle 24-34.509, Jussieu

10h30 - Accueil Café

11H00 - Séminaire

Orateur : Patrick Hennebelle (CEA Saclay)

Titre : The formation of protoplanetary discs and the critical role of non ideal MHD

Résumé :
It is now well understood that low mass stars form through the collapse of prestellar dense cores. It is believed that due to the conservation of angular momentum, a centrifugally supported disk, which eventually gives birth to planets, forms around the protostar. The conditions under which this exactly happens remains however a subject of active research. Observationally it is difficult to disentangle the collapsing envelope and the young disk and it is only recently that accurate constraints have been obtained, revealing that most disks appear to be relatively small in size and significantly smaller that would be obtained if angular momentum was conserved. In parallel, much progress has been accomplished from the theory side. In particular it has been realized that magnetic field is most likely playing a fundamental role through magnetic braking. This latter is so efficient that it may even lead to the complete disappearance of the disk, an effect also known as catastrophic magnetic braking. During the talk, I will describe the various works that have been performed to study this process, stressing the key role played by non- ideal MHD phenomena in particular the so-called ambipolar diffusion, that is to say, the decoupling between neutrals and ions, which limits the strength of the magnetic field and may even regulate the formation of the discs.

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CNRS Ecole Polytechnique Sorbonne Université Université Paris-Saclay Observatoire de Paris
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Directeur de la publication : Dominique Fontaine (Directrice)