Nuclear condensate and helium white dwarfs

TL;DR

This paper explores a novel quantum phase of helium in white dwarf cores, revealing a new gapless quasiparticle that significantly affects the star's thermal properties and cooling behavior.

Contribution

It identifies a previously unnoticed gapless quasiparticle in helium condensates within white dwarf cores, impacting their specific heat and cooling rates.

Findings

Discovery of a new gapless quasiparticle in helium condensates.

Specific heat in the condensed phase is two orders of magnitude smaller.

Potential observable effects on white dwarf cooling rates.

Abstract

We consider a high density region of the helium phase diagram, where the nuclei form a Bose-Einstein condensate rather than a classical plasma or a crystal. Helium in this phase may be present in helium-core white dwarfs. We show that in this regime there is a new gapless quasiparticle not previously noticed, arising when the constraints imposed by gauge symmetry are taken into account. The contribution of this quasiparticle to the specific heat of a white dwarf core turns out to be comparable in a range of temperatures to the contribution from the particle-hole excitations of the degenerate electrons. The specific heat in the condensed phase is two orders of magnitude smaller than in the uncondensed plasma phase, which is the ground state at higher temperatures, and four orders of magnitude smaller than the specific heat that an ion lattice would provide, if formed. Since the specific heat of the core is an important input for setting the rate of cooling of a white dwarf star, it may turn out that such a change in the thermal properties of the cores of helium white dwarfs has observable implications.