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

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Présentations pour les nouveaux arrivants au LERMA

Présentation 2020

Journée d’accueil des nouveaux arrivants du 18 novembre 2020 : Programme de la réunion : Thèmes abordés lors de la réunion :
1. Présentation générale du LERMA (B. Semelin) 2. Informations (...)

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Présentations 2017

Présentations faites lors de la journée des nouveaux arrivants le 8 décembre 2017 :
Présentation générale du laboratoire (Darek Lis)
Informations administratives et financières (Valérie Audon et (...)

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Présentations 2018

Thèmes abordés lors de la journée des nouveaux arrivants le 19 novembre 2018 :
Présentation générale du laboratoire (Darek Lis)
Informations administratives et financières (Murielle Chevrier & (...)

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Règlement Intérieur du LERMA

Toute personne travaillant au LERMA doit avoir pris connaissance du Règlement Intérieur de l’Unité : Accusé de lecture du Règlement Intérieur à signer et à renvoyer à : carine.bingan @ (...)

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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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