There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

We substantially update the capabilities of the open-source software instrument Modules for Experiments in Stellar Astrophysics (MESA). MESA can now simultaneously evolve an interacting pair of differentially rotating stars undergoing transfer and loss of mass and angular momentum, greatly enhancing the prior ability to model binary evolution. New MESA capabilities in fully coupled calculation of nuclear networks with hundreds of isotopes now allow MESA to accurately simulate advanced burning stages needed to construct supernova progenitor models. Implicit hydrodynamics with shocks can now be treated with MESA, enabling modeling of the entire massive star lifecycle, from pre-main sequence evolution to the onset of core collapse and nucleosynthesis from the resulting explosion. Coupling of the GYRE non-adiabatic pulsation instrument with MESA allows for new explorations of the instability strips for massive stars while also accelerating the astrophysical use of asteroseismology data. We improve treatment of mass accretion, giving more accurate and robust near-surface profiles. A new MESA capability to calculate weak reaction rates "on-the-fly" from input nuclear data allows better simulation of accretion induced collapse of massive white dwarfs and the fate of some massive stars. We discuss the ongoing challenge of chemical diffusion in the strongly coupled plasma regime, and exhibit improvements in MESA that now allow for the simulation of radiative levitation of heavy elements in hot stars. We close by noting that the MESA software infrastructure provides bit-for-bit consistency for all results across all the supported platforms, a profound enabling capability for accelerating MESA's development.

https://iopscience.iop.org/article/10.1088/0067-0049/220/1/15/pdf

Modules for experiments in stellar astrophysics (mesa): binaries, pulsations, and explosions

Modules for Experiments in Stellar Astrophysics (MESA): Binaries, Pulsations, and Explosions

心臓病診療プラクティス 16. 心不全を癒す

We update the capabilities of the software instrument Modules for Experiments in Stellar Astrophysics (MESA) and enhance its ease of use and availability. Our new approach to locating convective boundaries is consistent with the physics of convection, and yields reliable values of the convective-core mass during both hydrogen- and helium-burning phases. Stars with  become white dwarfs and cool to the point where the electrons are degenerate and the ions are strongly coupled, a realm now available to study with MESA due to improved treatments of element diffusion, latent heat release, and blending of equations of state. Studies of the final fates of massive stars are extended in MESA by our addition of an approximate Riemann solver that captures shocks and conserves energy to high accuracy during dynamic epochs. We also introduce a 1D capability for modeling the effects of Rayleigh–Taylor instabilities that, in combination with the coupling to a public version of the  radiation transfer instrument, creates new avenues for exploring Type II supernova properties. These capabilities are exhibited with exploratory models of pair-instability supernovae, pulsational pair-instability supernovae, and the formation of stellar-mass black holes. The applicability of MESA is now widened by the capability to import multidimensional hydrodynamic models into MESA. We close by introducing software modules for handling floating point exceptions and stellar model optimization, as well as four new software tools—  ,  -Docker,  , and mesastar.org—to enhance MESA's education and research impact.

https://iopscience.iop.org/article/10.3847/1538-4365/aaa5a8/pdf

Modules for Experiments in Stellar Astrophysics (MESA) : Convective Boundaries, Element Diffusion, and Massive Star Explosions

As a consequence of strong collective behavior, the microscopic dynamics of the one-component plasma (OCP) differs significantly from that of ordinary liquids. We show that, when particle caging dominates, the OCP transport coefficients nevertheless satisfy universal laws satisfied by dense ordinary fluids: the Stokes-Einstein relation, the Arrhenius law of viscosity, and several excess-entropy scaling relations. These results extend to long-range interaction potentials, the unifying description of atomic transport in condensed matter.

Liquid-state properties of a one-component plasma.

A plasma transport theory that spans weak to strong coupling is developed from a binary collision picture, but where the interaction potential is taken to be an effective potential that includes correlation effects and screening self-consistently. This physically motivated approach provides a practical model for evaluating transport coefficients across coupling regimes. The theory is shown to compare well with classical molecular dynamics simulations of temperature relaxation in electron-ion plasmas as well as simulations and experiments of self-diffusion in one-component plasmas. The approach is versatile and can be applied to other transport coefficients as well.

Effective Potential Theory for Transport Coefficients across Coupling Regimes

Molecular-dynamics simulations are used to investigate temperature relaxation between electrons and ions in a fully ionized, classical Coulomb plasma with minimal assumptions. Recombination is avoided by using like charges. The relaxation rate agrees with theory in the weak coupling limit ($g\ensuremath{\equiv}\mathrm{\text{potential}}/\mathrm{\text{kinetic energy}}\ensuremath{\ll}1$), whereas it saturates at $gg1$ due to correlation effects. The ``Coulomb log'' is found to be independent of the ion charge (at constant $g$) and mass ratio $g25$.

Molecular-dynamics simulations of electron-ion temperature relaxation in a classical Coulomb plasma.

Molecular-dynamics simulations are used to investigate temperature relaxation between electrons and ions in a fully ionized, classical Coulomb plasma with minimal assumptions. Recombination is avoided by using like charges. The relaxation rate agrees with theory in the weak coupling limit (g identical with potential/kinetic energy << 1), whereas it saturates at g > 1 due to correlation effects. The \"Coulomb log\" is found to be independent of the ion charge (at constant g) and mass ratio > 25.

Molecular Dynamics (MD) simulations of electron-ion temperature relaxation in a classical Coulomb plasma

We present a model for the rate of temperature relaxation between electrons and ions in plasmas. The model includes self-consistently the effects of particle screening, electron degeneracy, and correlations between electrons and ions. We successfully validate the model over a wide range of plasma coupling against molecular-dynamics simulations of classical plasmas of like-charged electrons and ions. We present calculations of the relaxation rates in dense hydrogen and show that, while electron-ion correlation effects are indispensable in classical, like-charged plasmas at any density and temperature, quantum diffraction effects prevail over electron-ion correlation effects in dense hydrogen plasmas.

Jérôme Daligault

Papers

Liquid-state properties of a one-component plasma.

Effective Potential Theory for Transport Coefficients across Coupling Regimes

Molecular-dynamics simulations of electron-ion temperature relaxation in a classical Coulomb plasma.

Molecular Dynamics (MD) simulations of electron-ion temperature relaxation in a classical Coulomb plasma

Correlation effects on the temperature-relaxation rates in dense plasmas.