White dwarfs and revelations

TL;DR

This study uses precise white dwarf measurements to constrain modified gravity theories, accounting for stellar composition effects, and improves existing bounds significantly.

Contribution

It provides the first detailed analysis incorporating composition and temperature effects to refine bounds on modified gravity using white dwarf data.

Findings

Bound on gravity modification parameter Y < 0.14 at 95% confidence

Improved constraints by a factor of three over previous studies

Identified degeneracies between gravity theories and stellar composition

Abstract

We use the most recent, complete and independent measurements of masses and radii of white dwarfs in binaries to bound the class of non-trivial modified gravity theories, viable after GW170817/GRB170817, using its effect on the mass-radius relation of the stars. We show that the uncertainty in the latest data is sufficiently small that residual evolutionary effects, most notably the effect of core composition, finite temperature and envelope structure, must now accounted for if correct conclusions about the nature of gravity are to be made. We model corrections resulting from finite temperature and envelopes to a base Hamada-Salpeter cold equation of state and derive consistent bounds on the possible modifications of gravity in the stars' interiors, finding that $Y< 0.14$ at 95\% confidence, an improvement of a factor of three with respect to previous bounds. Finally, our analysis reveals some fundamental degeneracies between the theory of gravity and the precise chemical makeup of white dwarfs.