White Dwarfs as Physics Laboratories: Lights and Shadows

Abstract

The evolution of white dwarfs is essentially a gravothermal process of cooling in which the basic ingredients for predicting their evolution are well identified, although not always well understood. There are two independent ways to test the cooling rate. One is the luminosity function of the white dwarf population, and another is the secular drift of the period of pulsation of those individuals that experience variations. Both scenarios are sensitive to the cooling or heating time scales, for which reason, the inclusion of any additional source or sink of energy will modify these properties and will allow to set bounds to these perturbations. These studies also require complete and statistical significant samples for which current large data surveys are providing an unprecedented wealth of information. In this paper we review how these techniques are applied to several cases like the secular drift of the Newton gravitational constant, neutrino magnetic moments, axions and weakly interacting massive particles (WIMPS).

Structure and evolution of ultra-massive white dwarfs in general relativity

“…Therefore, these old stellar remnants contain valuable information on the stellar evolution theory, the kinematics and the star formation history of our Galaxy, and the ultimate fate of planetary systems (see Winget & Kepler 2008;Althaus et al 2010;García-Berro & Oswalt 2016;Córsico et al 2019a, for reviews). Furthermore, given the large densities that characterize the white dwarf interiors, these compact objects are considered reliable cosmic laboratories to study the properties of baryonic matter under extreme physical conditions (Isern et al 2022). Among all the white dwarfs, of special interest are the socalled ultra-massive white dwarfs, defined as those with masses larger than ∼ 1.05M .…”

Looking into dark matter with asteroseismology

“…Therefore an excess in the rate of change of the period exists. This is the case of the pulsating WD G117-B15A (Figure 6), a ZZ Ceti object Isern et al (2022); Córsico et al (2019). For this white dwarf the discrepancy between the standard theory and the observations has been explained with the inclusion in the models of an additional cooling process, due to axion emission (Isern et al, 2022).…”

“…This is the case of the pulsating WD G117-B15A (Figure 6), a ZZ Ceti object Isern et al (2022); Córsico et al (2019). For this white dwarf the discrepancy between the standard theory and the observations has been explained with the inclusion in the models of an additional cooling process, due to axion emission (Isern et al, 2022). If an additional axion cooling is included for G117-B15A, the energy, ϵ eff changes, according to Eq 6.…”

“…About this last topic, it is worth mentioning that the period variation of the stellar pulsations have been proposed in order to study the size variation of the internal cavities of the stars, which is related to the convective transport, (Kurtz, 2022). Moreover, the measured change of periods of some white dwarfs has been proposed as a way to look into their radiative cooling mechanisms, constraining also some dark matter properties, like the mass of the axion (Isern and García-Berro, 2008;Isern et al, 2022).…”

“…Stellar interiors are suitable environments to expect the production, accretion, and/or annihilation of dark matter (Raffelt and Dearborn, 1987;Córsico et al, 2001;Iocco, 2008;Isern and García-Berro, 2008;Scott et al, 2008;Taoso et al, 2008;Córsico et al, 2012;Vinyoles et al, 2015;Isern et al, 2022), and the star life times are long enough to be affected by continous emission fluxes of dark matter from their interiors. Thus, the observables related to stars and stellar populations can be significantly modified when dark matter is introduced in the stellar models (Scott et al, 2008;Taoso et al, 2008;Casanellas and Lopes, 2011;Ayala et al, 2014).…”