Tomaschitz, R.
(2018). White dwarf stars exceeding the Chandrasekhar mass limit, *Physica A*
**489**, 128-140, DOI: 10.1016/j.physa.2017.07.024

**Abstract (**ScienceDirect**, **SAO/NASA ADS**)**

The effect of nonlinear ultra-relativistic electron dispersion on the mass-radius relation of high-mass white dwarfs is studied. The dispersion is described by a permeability tensor in the Dirac equation, generated by the ionized high-density stellar matter, which constitutes the neutralizing background of the nearly degenerate electron plasma. The electron dispersion results in a stable mass-radius relation for high-mass white dwarfs, in contrast to a mass limit in the case of vacuum permeabilities. In the ultra-relativistic regime, the dispersion relation is a power law whose amplitude and scaling exponent is inferred from mass and radius estimates of two high-mass white dwarfs, Sirius B and LHS 4033. Evidence for the existence of super-Chandrasekhar mass white dwarfs is provided by several Type Ia supernovae (e.g., SN 2013cv, SN 2003fg, SN 2007if and SN 2009dc), whose mass ejecta exceed the Chandrasekhar limit by up to a factor of two. The dispersive mass-radius relation is used to estimate the radii, central densities, Fermi temperatures, bulk and compression moduli and sound velocities of their white dwarf progenitors.

05.30.Fk Fermion systems and electron gas

05.70.Ce Thermodynamic functions and equations of state

95.30.Tg Thermodynamic processes, conduction, convection, equations of state

97.20.Rp Faint blue stars, white dwarfs, degenerate stars, nuclei of planetary nebulae

97.60.Bw Supernovae

description: Roman
Tomaschitz (2018) White dwarf stars exceeding the Chandrasekhar mass limit, *Physica
A ***489**, 128.

**Keywords:** Nearly degenerate
ultra-relativistic electron plasma; Quantum densities with power-law dispersion
and Weibull spectral decay; Dirac equation coupled to a permeability tensor;
Mechanical and thermal stability of a dispersive Fermi gas at low temperature;
Mass-radius relation of high-mass white dwarfs; Progenitors of
super-Chandrasekhar mass thermonuclear supernovae

**Highlights**

A nearly degenerate electron plasma pervading an ionized high-density background medium is studied, as it occurs in stellar matter.

The Dirac equation coupled to the permeability tensor of the medium leads to nonlinear electron dispersion in the ultra-relativistic regime.

The quantized spectral density of a low-temperature electron gas in a dispersive medium is shown to be mechanically and thermally stable.

The nonlinear electron dispersion affects the mass-radius relation of white dwarfs, whose mass can surpass the Chandrasekhar limit.

White dwarf progenitors of super-Chandrasekhar mass Type Ia supernovae: estimates of their central mass density, incompressibility and speed of sound.

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