The white dwarf luminosity function

TL;DR

The paper reviews recent empirical determinations and theoretical modeling of the white dwarf luminosity function, highlighting its importance for understanding Galactic evolution, dark matter, and fundamental physics.

Contribution

It provides a comprehensive overview of observational and theoretical approaches to the white dwarf luminosity function, including recent advances and remaining uncertainties.

Findings

Empirical white dwarf luminosity functions have been recently determined for different Galactic populations.

Theoretical models of white dwarf cooling sequences are crucial for interpreting luminosity functions.

White dwarf luminosity functions can constrain Galactic history, dark matter, and fundamental physics.

Abstract

White dwarfs are the final remnants of low- and intermediate-mass stars. Their evolution is essentially a cooling process that lasts for $\sim 10$ Gyr. Their observed properties provide information about the history of the Galaxy, its dark matter content and a host of other interesting astrophysical problems. Examples of these include an independent determination of the past history of the local star formation rate, identification of the objects responsible for the reported microlensing events, constraints on the rate of change of the gravitational constant, and upper limits to the mass of weakly interacting massive particles. To carry on these tasks the essential observational tools are the luminosity and mass functions of white dwarfs, whereas the theoretical tools are the evolutionary sequences of white dwarf progenitors, and the corresponding white dwarf cooling sequences. In particular, the observed white dwarf luminosity function is the key manifestation of the white dwarf cooling theory, although other relevant ingredients are needed to compare theory and observations. In this review we summarize the recent attempts to empirically determine the white dwarf luminosity function for the different Galactic populations. We also discuss the biases that may affect its interpretation. Finally, we elaborate on the theoretical ingredients needed to model the white dwarf luminosity function, paying special attention to the remaining uncertainties, and we comment on some applications of the white dwarf cooling theory. Astrophysical problems for which white dwarf stars may provide useful leverage in the near future are also discussed.