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

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Interstellar Medium and Plasmas

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What processes drive the evolution of interstellar matter in the Milky Way and in other galaxies ? What roles do the turbulence, the magnetic field, the cosmic rays, and the radiation field play in this evolution ? Those fundamental questions for modern Astrophysics now appear at many spatial scales and for a great variety of environments : from the galactic scales where the diffuse gas collapse to form the precursors of new stars ; down to the scale of proto-planetary disks where the central star strongly interacts with the surrounding matter ; and even in the stars themselves where the transport mechanisms are still unknown. To study all these astronomical objects, the group « Interstellar Medium and Plasmas » of the LERMA combine theoretical works, numerical modeling, 3D simulations, and observations of interstellar environments at high spectral and angular resolutions.

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On the observational side, our group is specialized in the treatment and the analysis of the data obtained with the most advanced space and ground-based observatories. Our expertise is particularly strong in the infrared and sub-millimeter domains which reveal the emission of atoms, molecules and interstellar dust. We have therefore been deeply involved in the recent successes and findings of Herschel and Planck space observatories, which we now follow up by collecting data with the new generation of instruments (in particular, APEX, ALMA, and soon NOEMA).

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On the numerical side, the codes developed in our group are internationally renowned as state-of-the-art tools for the analysis of interstellar matter and the interpretation of observational data. Our expertise extends from the conception of 3D numerical simulations of magnetohydrodynamics, which we run using high-level computational capacities (e.g. PRACE, MesoPSL), to the development of advanced numerical models. The strength of those models, which we provide to the community through the ISM and jets platform, is to solve a great number of microphysical processes at play in the interstellar medium, with prescriptions based on the results of laboratory experiments and theoretical studies which are partly performed in our laboratory.

Select one of the following links to know more about our activities

1. Turbulence & magnetic field

2. Matter / photon interactions

3. Stellar plasmas and laboratory astrophysics

4. Prestellar cores

5. Protostars, debris & jets

6. Accretion & ejection in stars

Click here to access our publications

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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