Laboratoire d’Études du Rayonnement et de la Matière en Astrophysique et Atmosphères

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Proto-étoiles, disques & jets

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Jets protostellaires : propriétés chimiques et dynamiques

Au stade protostellaire, les effets combinés de la rotation et du champ magnétique conduisent à la formation de jets lancés dans l’environnement immédiat des embryons stellaires. L’étude de ces jets et des flots moléculaires qui tracent l’interaction des jets avec le milieu ambiant, apporte des informations incomparables sur le processus de formation des étoiles. Nous étudions en particulier les chocs associés à ces jets, les phénomènes physiques et chimiques associés, qui permettent de remonter aux processus d’accrétion.

Disques de débris dans les systèmes planétaires

Un disque protostellaire et formé en même temps que la proto-étoile, dont l’évolution se poursuit en parallèle de celle de l’objet protostellaire. L’étude de ces disques autour des étoiles jeunes apporte des clés pour comprendre la formation des planètes.

Formation des étoiles massives

Séminaires à venir

Vendredi 23 avril 2021, 14h00
Visioconférence, VIDEO
A stellar graveyard in the core of a globular cluster
résumé :
The ubiquity of supermassive black holes in massive galaxies suggests the existence of intermediate-mass ones (IMBHs) in smaller systems. However, IMBHs are at best rare in dwarf galaxies and not convincingly seen in globular clusters. We embarked on a search for such an IMBH in a very nearby core-collapsed globular cluster, NGC 7397. For this we ran extensive mass-orbit modeling with our Bayesian MAMPOSSt-PM code that fits mass and velocity anisotropy models to the distribution of observed tracers in 4D projected phase space. We used a combination of proper motions from HST and Gaia, supplemented with redshifts from MUSE. We found very strong Bayesian evidence for an excess of unseen mass in the core of the cluster amounting to 1 to 2% of the cluster mass. But surprisingly, we found rather strong evidence that this excess mass is not point-like but has a size of roughly 3% of that of the cluster. Our conclusion is robust to our adopted surface density profile and on our modeling of the velocity anisotropy, as the data suggest isotropic orbits throughout the cluster. It is also robust to our use of one or two classes of Main Sequence stars (given the mass segregation in collisional systems such as clusters), as well as on our filtering for quality data. The expected mass segregation suggests that the excess mass is made of objects heavier than Main Sequence stars: white dwarfs, neutron stars and possibly stellar black holes, all of which lost their orbital energy by dynamical friction to end up in the cluster core. I will discuss the evidence for and against the possibility that most of the unseen mass in the center is in the form of such black holes, as well as the consequences of this intriguing possibility.
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