LAUSR

The fine structure constant α sets the strength of the electromagnetic force. The Standard Model of particle physics provides no explanation for its value, which could potentially vary. The wavelengths of stellar absorption lines depend on α but are subject to systematic effects owing to astrophysical processes in stellar atmospheres. We measured precise line wavelengths from observations of 17 stars, selected to have almost identical atmospheric properties to those of the Sun (solar twins), which reduces those systematic effects. We found that α varies by ≲50 parts per billion within 50 parsecs from Earth. Combining the results from all 17 stars provides an empirical local reference for stellar measurements of α, with an ensemble precision of 12 parts per billion. Description Stars constrain the fine structure constant The strength of the electromagnetic force is quantified by the fine structure constant α. The Standard Model of particle physics provides no explanation for its value, which could conceivably vary from place to place. Murphy et al. have used spectra of 17 nearby stars, with properties matched to the Sun, to investigate absorption lines that are sensitive to α. They set an upper limit of 50 parts per billion on variations of α between the stars. The results rule out substantial changes in α within the local region of the Milky Way, filling a gap between laboratory measurements and constraints from the distant Universe. —KTS Absorption lines in nearby stars set a limit of 50 parts per billion on variations of the fine structure constant.