Indication of the electron-to-proton mass ratio variation within the Galaxy

Abstract

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 mu=m_e/m_p - the electron-to-proton mass ratio. Measured frequency difference between the emission lines of methanol (CH3OH), - J_K_u - J_K_l = 6_3 - 5_2 A+ 542000.981 MHz, 6_3 - 5_2 A- 542081.936 MHz, and 8_0 - 7_-1 E 543076.194 MHz, - observed with the space observatory Herschel toward SgrB2(N) and Orion-KL corresponds to (Sgr-Ori): Delta mu/mu = (-3.7 +/- 0.5)*10^(-7) (1 sigma C.L.). At the same time, comparison of the same methanol lines in Orion-KL with laboratory frequencies shows no significant changes in mu (Ori-lab): Delta mu/mu = (-0.5 +/- 0. 6)*10^(-7), while a comparison between SgrB2(N) and laboratory lines indicates a lower value of mu near the Galactic center (Sgr-lab): Delta mu/mu = (-4.2 +/- 0.7)*10^(-7). The reduced value of mu in SgrB2(N) is not explained by known systematic effects and requires further investigation.

11 pages, 1 figure, 3 tables, accepted for publication in JETP Letters, vol. 121, issue 8