LERMA UMR8112

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



Accueil > fr > Intranet > Conseil de Laboratoire > Réunions 2016

11 Juillet

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Conseil de laboratoire du LERMA
11 juillet 2016 à 9h30
Observatoire de Paris
Salle Danjon
77, avenue Denfert Rochereau
75014 Paris


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ORDRE DU JOUR



I Approbation de l’ordre du jour



II Approbation du compte rendu du Conseil de laboratoire du 3 mai 2016



III Informations du Directeur



IV Examen des demandes de "visiteurs longue durée"



V Budget : point sur l’état des dépenses



VI Poursuite de la discussion sur les missions du directeur technique


VI Questions diverses

Relevé de conclusions
Compte rendu

Séminaires à venir

Vendredi 23 avril 2021, 14h00
Visioconférence, VIDEO
A stellar graveyard in the core of a globular cluster
Gary MAMON
IAP
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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