Search for a Variation of the Fine Structure Constant around the Supermassive Black Hole in Our Galactic Center

Searching for space-time variations of the constants of Nature is a promising way to search for new physics beyond general relativity and the standard model motivated by unification theories and models of dark matter and dark energy. We propose a new way to search for a variation of the fine-structure constant using measurements of late-type evolved giant stars from the S star cluster orbiting the supermassive black hole in our Galactic Center. A measurement of the difference between distinct absorption lines (with different sensitivity to the fine structure constant) from a star leads to a direct estimate of a variation of the fine structure constant between the star’s location and Earth. Using spectroscopic measurements of five stars, we obtain a constraint on the relative variation of the fine structure constant below ${10}^{-5}$. This is the first time a varying constant of nature is searched for around a black hole and in a high gravitational potential. This analysis shows new ways the monitoring of stars in the Galactic Center can be used to probe fundamental physics.

Figure 1

Left: the gravitational potential probed by several searches for varying $\alpha$ against the mass of the central body that generates gravity in these tests. Right: the compactness $\mathrm{\Xi }=GM/c^{2}R$ of the central body probed by several searches for varying $\alpha$ against the gravitational potential. Searches for varying $\alpha$ with S stars explore a new region in this parameter space.

Figure 2

Representation of the motion of the five stars considered in our analysis between 1995 and 2018. The large stars represent the positions of the stars in 2018. All these stars have a magnitude brighter than $M=15$. S0-6, S0-12, S0-13, S1-5 have been measured spectroscopically with the NIFS instrument with Gemini in 2018, S0-6 was also measured with the IRCS instrument from Subaru in 2018 and S1-23 with the NIRSPEC instrument at Keck in 2016.

Figure 3

Example spectra of the stars used in this work. Left: Spectrum of the star S0-6 observed using the NIFS spectrograph with a spectral resolution $R=5000$. We have identified three lines that are suitable for the fine structure constant analysis. Center and right: Spectra of the star S1-23 observed with the NIRSPEC instrument with $R=20000$. This higher spectral resolution allows us to identify ten atomic lines for use in this experiment.