A measurement of the equation of state of carbon envelopes of white dwarfs

Andrea L. Kritcher (), Damian C. Swift, Tilo Döppner, Benjamin Bachmann, Lorin X. Benedict, Gilbert W. Collins, Jonathan L. DuBois, Fred Elsner, Gilles Fontaine, Jim A. Gaffney, Sebastien Hamel, Amy Lazicki, Walter R. Johnson, Natalie Kostinski, Dominik Kraus, Michael J. MacDonald, Brian Maddox, Madison E. Martin, Paul Neumayer, Abbas Nikroo, Joseph Nilsen, Bruce A. Remington, Didier Saumon, Phillip A. Sterne, Wendi Sweet, Alfredo A. Correa, Heather D. Whitley, Roger W. Falcone and Siegfried H. Glenzer
Additional contact information
Andrea L. Kritcher: Lawrence Livermore National Laboratory
Damian C. Swift: Lawrence Livermore National Laboratory
Tilo Döppner: Lawrence Livermore National Laboratory
Benjamin Bachmann: Lawrence Livermore National Laboratory
Lorin X. Benedict: Lawrence Livermore National Laboratory
Gilbert W. Collins: Lawrence Livermore National Laboratory
Jonathan L. DuBois: Lawrence Livermore National Laboratory
Fred Elsner: General Atomics
Gilles Fontaine: Université de Montréal, Montreal
Jim A. Gaffney: Lawrence Livermore National Laboratory
Sebastien Hamel: Lawrence Livermore National Laboratory
Amy Lazicki: Lawrence Livermore National Laboratory
Walter R. Johnson: University of Notre Dame
Natalie Kostinski: Lawrence Livermore National Laboratory
Dominik Kraus: Helmholtz-Zentrum Dresden-Rossendorf
Michael J. MacDonald: Lawrence Livermore National Laboratory
Brian Maddox: Lawrence Livermore National Laboratory
Madison E. Martin: Lawrence Livermore National Laboratory
Paul Neumayer: GSI Helmholtzzentrum für Schwerionenforschung GmbH
Abbas Nikroo: Lawrence Livermore National Laboratory
Joseph Nilsen: Lawrence Livermore National Laboratory
Bruce A. Remington: Lawrence Livermore National Laboratory
Didier Saumon: Los Alamos National Laboratory
Phillip A. Sterne: Lawrence Livermore National Laboratory
Wendi Sweet: General Atomics
Alfredo A. Correa: Lawrence Livermore National Laboratory
Heather D. Whitley: Lawrence Livermore National Laboratory
Roger W. Falcone: University of California Berkeley
Siegfried H. Glenzer: SLAC National Accelerator

Nature, 2020, vol. 584, issue 7819, 51-54

Abstract: Abstract White dwarfs represent the final state of evolution for most stars1–3. Certain classes of white dwarfs pulsate4,5, leading to observable brightness variations, and analysis of these variations with theoretical stellar models probes their internal structure. Modelling of these pulsating stars provides stringent tests of white dwarf models and a detailed picture of the outcome of the late stages of stellar evolution6. However, the high-energy-density states that exist in white dwarfs are extremely difficult to reach and to measure in the laboratory, so theoretical predictions are largely untested at these conditions. Here we report measurements of the relationship between pressure and density along the principal shock Hugoniot (equations describing the state of the sample material before and after the passage of the shock derived from conservation laws) of hydrocarbon to within five per cent. The observed maximum compressibility is consistent with theoretical models that include detailed electronic structure. This is relevant for the equation of state of matter at pressures ranging from 100 million to 450 million atmospheres, where the understanding of white dwarf physics is sensitive to the equation of state and where models differ considerably. The measurements test these equation-of-state relations that are used in the modelling of white dwarfs and inertial confinement fusion experiments7,8, and we predict an increase in compressibility due to ionization of the inner-core orbitals of carbon. We also find that a detailed treatment of the electronic structure and the electron degeneracy pressure is required to capture the measured shape of the pressure–density evolution for hydrocarbon before peak compression. Our results illuminate the equation of state of the white dwarf envelope (the region surrounding the stellar core that contains partially ionized and partially degenerate non-ideal plasmas), which is a weak link in the constitutive physics informing the structure and evolution of white dwarf stars9.

Date: 2020
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DOI: 10.1038/s41586-020-2535-y

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