First semi-empirical test of the white dwarf mass–radius relationship using a single white dwarf via astrometric microlensing

In November 2019, the nearby single, isolated DQ-type white dwarf LAWD 37 (WD 1142-645) aligned closely with a distant background source and caused an astrometric microlensing event. Leveraging astrometry from \Gaia{} followup data \textit{Hubble Space Telescope} we measure deflection of obtain gravitational mass for LAWD~37. The main challenge this analysis is in extracting lensing signal faint whilst it buried wings LAWD~37's point spread function. Removal 37's function induces significant amount correlated noise which find can mimic signal. We model including by removal best explains yields $0.56\pm0.08 M_{\odot}$. This agreement theoretical mass-radius relationship cooling tracks expected CO core dwarfs. Furthermore, consistent no or trace amounts hydrogen that objects helium-rich atmospheres like 37. conclude further on likely to improve inference at $\approx3$ percent level definitively rule out purely explanations data. work provides first semi-empirical test using supports current DQ dwarfs evolutionary theory.