The gravitational redshift of solar-type stars from Gaia DR3 wide binaries

TL;DR

This study demonstrates the direct measurement of gravitational redshift in solar-type stars using Gaia DR3 data, confirming predictions of general relativity in a new stellar context.

Contribution

The paper provides the first clear detection of gravitational redshift in main-sequence stars through Gaia DR3 radial velocities of wide binary systems.

Findings

Giant stars' RVs are on average 0.49 km/s lower than their main-sequence companions.

The measured redshift aligns with general relativity predictions.

Gravitational redshift is detectable in solar-type stars with Gaia data.

Abstract

Light escaping from a gravitational potential suffers a redshift with magnitude proportional to the depth of the potential. This "gravitational redshift" is easily measurable in dense stars such as white dwarfs, but is much weaker and has evaded unambiguous detection in main-sequence stars. I show that the effect is directly measurable in the Gaia DR3 radial velocities (RVs) of the components of wide binary stars. In a sample of $\sim$500 wide binaries containing a solar-type main-sequence star and a red giant or red clump companion, the apparent RV of the giant is on average $0.49 \pm 0.02 \,\, \rm km\,s^{-1}$ lower than that of the main-sequence star. This owes primarily to the giants' weaker gravitational fields and is in reasonably good agreement with the value expected from general relativity.