Relativistic deflection of background starlight measures the mass of a nearby white dwarf star

TL;DR

This paper measures the mass of a nearby white dwarf star using gravitational microlensing observed with the Hubble Space Telescope, confirming theories of degenerate matter and white dwarf evolution.

Contribution

It demonstrates a novel application of astrometric microlensing with space-based telescopes to determine stellar masses.

Findings

White dwarf Stein 2051 B mass: 0.675 +/- 0.051 solar masses

First use of Hubble for astrometric microlensing to measure stellar mass

Supports existing theories of white dwarf physics

Abstract

Gravitational deflection of starlight around the Sun during the 1919 total solar eclipse provided measurements that confirmed Einstein's general theory of relativity. We have used the Hubble Space Telescope to measure the analogous process of astrometric microlensing caused by a nearby star, the white dwarf Stein 2051 B. As Stein 2051 B passed closely in front of a background star, the background star's position was deflected. Measurement of this deflection at multiple epochs allowed us to determine the mass of Stein 2051 B -- the sixth nearest white dwarf to the Sun -- as 0.675 +/- 0.051 solar masses. This mass determination provides confirmation of the physics of degenerate matter and lends support to white dwarf evolutionary theory.