Constraints on the dark mass distribution surrounding Sgr A*: simple $\chi^2$ analysis for the redshift of photons from orbiting stars

Understand

Sagittarius A* (Sgr A*) is the central supermassive black hole with the mass $\sim 4\times 10^6 M_{\odot}$ in the Milky Way and stars are orbiting around it.

• In May 2018, one of the nearest stars to Sgr A* named S0-2/S2 experienced the pericenter passage.
• The redshift of photons from S0-2 had varied from $4000\>{\rm km\>s^{-1}}$ to $-2000\>{\rm km\>s^{-1}}$ during the pericenter passage, which is within $0.5\>{\rm yr}$.
• In this paper, we show that this steep variation of the redshift gives a strong constraint on a dark mass distribution inside the orbit of S0-2.