LERMA UMR8112

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



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Where are we located ?

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LERMA is situated on 4 sites in the Paris region :

  • Paris Observatory
  • Meudon Observatory
  • Sorbone University (UPMC)
  • Cergy Paris University (CYU)




Paris Observatory : Paris site

- Postal address : 61, avenue de l’Observatoire - 75014 Paris
- Pedestrian and vehicular access : 77, Avenue Denfert-Rochereau - 75014 Paris
- Telephone : +33 1 40 51 22 21
- Fax : +33 1 43 54 18 04
- Observatory web site
- Access





Paris Observatory : Meudon site

- Postal address and pedestrian access : Paris Observatory, Meudon site - 5, place Jules Janssen - 92195 Meudon Cedex - France
- Vehicle access and deliveries : 11, avenue Marcelin Berthelot - 92195 Meudon
- Telephone : +33 1 45 07 75 30
- Observatory web site
- Access


Sorbonne University - UPMC


- Postal address and pedestrian access : UPMC - box courrier 76 - 4 place Jussieu - 75252 Paris Cedex 05 - France
- Delivery address : Sorbonne University - Pierre and Marie Curie Campus
7 quai Saint-Bernard - 75252 Paris Cedex 05 - France
- Tower 32-33 2nd and 3rd floor
- Tower 24-34 5th floor
- Telephone : +33 1 44 27 44 27
- Website of Sorbonne University
- Access




University of Cergy Paris


- Postal address : LERMA/LAMAP - Neuville II site - UFR Sciences et Techniques - Physics Department - 5, mail Gay Lussac - 95000 Neuville-sur-Oise
- Telephone : +33 1 34 25 68 30
- Fax : +33 1 34 25 70 95
- Website of Cergy Paris Université
- Access

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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