Red dwarf stars are the most abundant stars in our galactic neighborhood, but the physics of their interiors is not well understood. Heat is generated in the core and travels outward to the surface, but it is not clear whether that process occurs via radiation, convection, or a combination of the two. The key factor determining whether red dwarfs are radiation- or convection-dominated is the opacity of the interior hydrogen.

Lütgert et al. devised an experiment to probe the opacity of hydrogen under conditions found in the interior of red dwarfs. The experimental setup is designed around a modified indirect drive inertial confinement fusion experiment at the National Ignition Facility.

The researchers are planning to measure the opacity of dense hydrogen due to free-free absorption, thought to be the dominant absorption mechanism for that environment. To accomplish this, the reaction will be modified to run at colder temperatures than required for self-sustaining inertial confinement fusion reactions, and the implosion will be probed by x-rays.

“We intend to perform a measurement of the hydrogen’s opacity by recording highly-resolved, nearly monochromatic x-ray radiographs of the implosion,” said author Julian Lütgert.

The experiment could improve our understanding of the most common type of star in the universe and possibly the planets that orbit them.

“We hope that our experiment can not only provide insight into the structure of red dwarf stars but also benchmark models that are widely used in high-energy-density physics and astrophysics,” said Lütgert.

Source: “Platform for probing radiation transport properties of hydrogen at conditions found in the deep interiors of red dwarfs,” by J. Lütgert, M. Bethkenhagen, B. Bachmann, L. Divol, D. O. Gericke, S. H. Glenzer, G. N. Hall, N. Izumi, S. F. Khan, O. L. Landen, S. A. MacLaren, L. Masse, R. Redmer, M. Schörner, M. O. Schölmerich, S. Schumacher, N. R. Shaffer, C. E. Starrett, P. A. Sterne, C. Trosseille, T. Döppner, and D. Kraus, Physics of Plasmas (2022). The article can be accessed at