Energy produced in the sun’s core passes through large amounts of ionised material, or plasma, to reach the solar surface from where it is radiated away. This energy transport occurs either through radiation or through convection. How efficiently energy is transferred by radiation and where radiation gives way to convection depends on how opaque the stellar plasma is.
Recent advances in laser technology have allowed researchers to reproduce, for short times and small samples, conditions similar to those found in the interior of stars. This allows experiments like the Z facility at the Sandia National Laboratories in New Mexico, U.S., to simulate stellar opacity, the absorption of radiation as it travels from the star’s core to the surface. Using the Z facility, Taisuke Nagayama from Sandia Labs and colleagues measured the contribution to opacities due to iron, chromium and nickel at the high densities and temperatures found in the solar interior. While the experiment confirmed a 2015 measurement at the Z facility that had focussed on iron only, the new team found large discrepancies between measured and modelled opacity values for all these elements. This means that stellar opacity calculations are far from correct and that our present understanding of the sun and stars is less clear than scientists believed. The results raise questions about the accuracy of solar models and call for more measurements to address the puzzle. Specifically, future experiments will need to measure the absorption of the gases oxygen and neon, which are major contributors to stellar opacity, the researchers said.