Indication of the Electron-to-Proton Mass Ratio Variation in the Galaxy

Near (~100 pc) and far (~8.7 kpc) relative to the Galactic center, the molecular clouds SgrB2(N) and Orion-KL exhibit different values of the fundamental physical constant μ = m e / m p , which is the electron-to-proton mass ratio. Measured frequency difference between the emission lines of methanol (CH 3 OH), $${{J}_{{{{K}_{u}}}}}$$ → $${{J}_{{{{K}_{\ell }}}}}$$ = 6 3 → 5 2 A + 542 000.981 MHz, 6 3 → 5 2 A – 542 081.936 MHz, and 8 0 → 7 –1 E 543 076.194 MHz, observed with the space observatory Herschel toward SgrB2(N) and Orion-KL corresponds to (Sgr-Ori): Δμ/μ = (‒3.7 ± 0.5) × 10 –7 (1σ C.L.). At the same time, comparison of the same methanol lines in Orion-KL with laboratory frequencies shows no significant changes in μ (Ori-lab): Δμ/μ = (–0.5 ± 0.6) × 10 –7 , while a comparison between SgrB2(N) and laboratory lines indicates a lower value of μ near the Galactic center (Sgr-lab): Δμ/μ = (–4.2 ± 0.7) × 10 –7 . The reduced value of μ in SgrB2(N) is not explained by known systematic effects and requires further investigation.