Stars in the laboratory... or how to produce stardust

This approach opens up new perspectives for quantifying the formation and composition of dust in various astrophysical environments. This work is described in an article published in the journal Nature Astronomy on October 23, 2024.
While cosmic dust plays a crucial role in galactic evolution, from the interstellar medium to the stars, its formation is still poorly understood. It is indeed difficult to recreate stellar astrophysical conditions in the laboratory. This includes producing a multi-element gas of controlled composition and condensing it under conditions of equilibrium or disequilibrium at high temperatures (2,000 to 3,000 K). Although theoretical models exist, experimental data on the formation of complex dust grains from multi-element gas under extreme conditions is scarce.

To simulate stellar atmospheres, researchers used a large-volume AC plasma torch (Fig. 1). A gas mixture of chondritic composition, made from 600 g of chondrites sprayed in the plasma Ar-H2 mixture, was used for these condensation experiments. The vapor formed in the plasma then condensed along the temperature gradient in a condensation chamber almost a meter high. The condensates were then sampled along the thermal gradient and analyzed for chemistry and mineralogy.

The experimental data support a condensation scenario kinetically controlled by the gas flow, faithfully reproducing the formation of carbides, carbides and minerals.the formation of carbides, silicides, nitrides, sulfides, oxides and silicates corresponding to the sequence of mineral phases obtained by condensation under high-temperature conditions with high C/O ratios. These results confirm for the first time thermodynamic predictions for carbon-rich circumstellar media, and underline the importance of kinetic effects in dust formation. Our thermodynamic simulations also enable us to assess the influence of physico-chemical parameters, such as pressure, on the mineralogical composition of condensates, thus providing a robust theoretical framework for interpreting astrophysical observations.

This work is the result of a fruitful collaboration between the Nice laboratories: PERSEE of Mines Paris-PSL specialized in energy storage and conversion, CRHEA (CNRS/Université Côte d'Azur) specialized in materials for photonic, optoelectronic, microelectronic devices, GEOAZUR (Université Côte d'Azur/OCA/CNRS, IRD) specialized in Earth Sciences, LAGRANGE (Université Côte d'Azur/OCA/CNRS) specicialised in astrophysics and the Lyon laboratory LGL-TPE (ENS de Lyon/CNRS/ Université Lyon I/UJM) specialized in Earth Sciences. This experimental study used the PERSEE laboratory's plasma torch. For the record, it was a casual remark by a PERSEE colleague comparing the brightness of the lit plasma torch to starlight that launched this research project.

Fig. 1: Experimental set-up and thermal regime in the condensation chamber. Left: 240 kW three-electrode arc plasma torch (PERSEE, Mines ParisTech, Sophia Antipolis, France) in which 600 g of a 20 μm powder of ordinary chondrite NWA 869 was vaporized and condensed for one hour. Right: 3D thermal regime simulated inside the condensation chamber using ANSYS Fluent computational fluid dynamics software.

Research contact

Guy Libourel, Lagrange, Université Côte d'Azur, OCA, libou@oca.eu
Vandad-Julien Rohani, PERSEE, Mines Paris-PSL, vandad-julien.rohani@minesparis.psl.eu
Bernard Bourdon, LGL-TPE, CNRS, bernard.bourdon@ens-lyon.fr
Clément Ganino, Geoazur, Université Côte d'Azur, OCA, clement.ganino@univ-cotedazur.fr

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High-temperature dust formation in carbon-rich astrophysical environments. Guy Libourel, Marwane Mokhtari, Vandad-Julien Rohani, Bernard Bourdon, Clément Ganino, Eric Lagadec, Philippe Vennéguès, Vincent Guigoz, François Cauneau, Laurent Fulcheri, Nature Astronomy, October 2024, https://www.nature.com/articles/s41550-024-02393-7