Limits on a Gravitational Field Dependence of the Proton{Electron Mass Ratio from H2 in White Dwarf Stars

Abstract

Spectra of molecular hydrogen (H2) are employed to search for a possible proton-to-electron mass ratio (μ) dependence on gravity. The Lyman transitions of H2, observed with the Hubble Space Telescope towards white dwarf stars that underwent a gravitational collapse, are compared to accurate laboratory spectra taking into account the high temperature conditions (T ~ 13000 K) of their photospheres. We derive sensitivity coefficients Ki which define how the individual H2 transitions shift due to μ-dependence. The spectrum of white dwarf star GD133 yields a Δμ/μ constraint of (-2:7 ± 4:7stat ± 0:2sys) × 10-5 for a local environment of a gravitational potential φ ~ 10 4 φEarth, while that of G29-38 yields Δμ/μ = (-5:8 ± 3:8stat ± 0:3sys) × 10-5 for a potential of 2 × 10 4 φEarth.