Charged Condensate and Helium Dwarf Stars

TL;DR

This paper proposes that helium white dwarf cores may form a charged Bose-Einstein condensate instead of crystallizing, leading to unique quantum properties and potential observational signatures.

Contribution

It introduces the concept of a charged condensate in helium dwarf stars, contrasting with traditional crystallization models, and analyzes its physical properties and observational implications.

Findings

Helium dwarf cores may form a charged Bose-Einstein condensate.

The condensate exhibits a mass gap in bosonic excitations.

Low-temperature specific heat is dominated by electrons, not bosons.

Abstract

White dwarf stars composed of carbon, oxygen or heavier elements are expected to crystallize as they cool down below certain temperatures. Yet, simple arguments suggest that the helium white dwarf cores may not solidify, mostly because of zero-point oscillations of the helium ions that would dissolve the crystalline structure. We argue that the interior of the helium dwarfs may instead form a macroscopic quantum state in which the charged helium-4 nuclei are in a Bose-Einstein condensate, while the relativistic electrons form a neutralizing degenerate Fermi liquid. We discuss the electric charge screening, and the spectrum of this substance, showing that the bosonic long-wavelength fluctuations exhibit a mass gap. Hence, there is a suppression at low temperatures of the boson contribution to the specific heat -- the latter being dominated by the specific heat of the electrons near the Fermi surface. This state of matter may have observational signatures.