| Abstract: We define `astromaterial science’ as the study of materials in astronomical objects that are qualitatively denser than materials on earth. Astromaterials can have unique properties related to their great density, though they may be organized like more conventional materials. By analogy to terrestrial materials, we divide our study of astromaterials into hard and soft and discuss one example of each. The hard astromaterial discussed here is a crystalline lattice, such as the Coulomb crystals in the interior of cold white dwarfs and in the crust of neutron stars, while the soft astromaterial is nuclear pasta found in the inner crusts of neutron stars. Coulomb crystals are studied to understand how compact stars freeze. Their incredible strength may make crust “mountains” on rotating neutron stars a source for gravitational waves that the Laser Interferometer Gravitational-Wave Observatory (LIGO) can detect. Nuclear pasta is expected near the base of the neutron star crust at densities of 10^14 g/cm^3. Competition between nuclear attraction and Coulomb repulsion rearranges neutrons and protons into complex non-spherical shapes such as sheets (lasagna) or tubes (spaghetti). Semi-classical molecular dynamics simulations of nuclear pasta are used to study these phases and calculate their transport properties such as neutrino opacity, thermal conductivity, and electrical conductivity. We compare nuclear pasta shapes with similar shapes seen in biological systems. We end by discussing the chemical separation of actinides such as uranium and thorium, as white dwarf material freezes. This might allow a natural nuclear chain reaction and ignite a supernova.
References: Rev. Mod. Phys. 89, 041002 (2017) and Phys. Rev. Lett. 126, 131101 (2021) |