What Are The Effects Of Temperature On Magnetic White Dwarfs? (Planetary Science)

Veronica Dexheimer and colleagues in their recent paper, studied the microscopic and macroscopic properties of white dwarfs. They model the interior of white dwarfs as a nuclei lattice surrounded by a relativistic free Fermi gas of electrons, accounting for effects from temperature and magnetic field. They found that, at low densities, both temperature and magnetic field effects play an important role in the calculation of microscopic thermodynamical quantities. Their study recently appeared in Arxiv.

Several studies modeled the core of white dwarf stars with one of the assumptions that the temperature or magnetic field can be disregarded. But, some recent observations suggested that a few white dwarfs may require the inclusion of both temperature and magnetic field effects in the calculation of the matter equation of state. In that light, Veronica Dexheimer and colleagues now examined for the first time, the effects of including both temperature and magnetic field into the equation of state of white dwarfs.

“To our knowledge, this is the first time that simultaneous effects of including both temperature and magnetic field in the equation of state for white dwarfs was investigated.”

— Veronica Dexheimer, one of the author of the study

Focusing first on microscopic quantities, they found that high temperatures tend to overpower the effects of magnetic fields which are expected to be seen in white dwarfs. While at lower temperatures, the magnetic field effects are more pronounced with very visible Van Alphen oscillations.

(Article continues below images)

FIG. 1. Left: (Color online) Magnetic field profile inside the most massive star of a sequence produced with current constant f0 = 10-³ in the polar direction as a function of energy density. Right: (Color online) The same as left panel but in the equatorial direction. © Dexheimer et al.
Fig 2: (Color online) Mass-radius diagram for sequences of stars produced within several temperature scenarios. Lines marked with an asterisk denote sequences with magnetic field effects generated by fixing a current constant f0 = 10-³ © Dexheimer et al.

Later, they numerically solved the Einstein Maxwell equations, in order to obtain results for macroscopic stellar properties, such as mass and radius, in the case of magnetic stars. They found that the strong magnetic fields they considered were not large enough to change properties such as stellar masses and radii, although a finite temperature magnetic field profile in different directions of the star was extracted.

“In the future, we intend on using these profiles to evaluate realistic magnetic field effects in, for example, pycnonuclear fusion reactions, and possibly on the crystalline structure of white dwarfs.

— concluded authors of the study

For more, refer:

J. Peterson, V. Dexheimer, R. Negreiros, B. G. Castanheira, “Effects of Magnetic Fields in Hot White Dwarfs”, Arxiv, pp. 1-10, 2021. https://arxiv.org/abs/2105.03387

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