Dark matter is undoubtedly one of the fundamental, albeit unknown, components of the standard cosmological model. The failure to detect weakly interacting massive particles, the most promising candidate particle for cold dark matter, actually opens the way for the exploration of viable alternatives of which ultralight bosonic particles with masses $\sim {10}^{-21}\mathrm{eV}$ represent one of the most encouraging. Numerical simulations have shown that such particles form solitonic cores in the innermost parts of virialized galactic halos that are supported by internal quantum pressure on characteristic $\sim \mathrm{kpc}$ de Broglie scales. In the Galaxy, this halo region can be probed by means of S-stars orbiting the supermassive black hole Sagittarius ${\mathrm{A}}^{*}$ to unveil the presence of such a solitonic core and, ultimately, to bound the boson mass $m_{\psi }$. Employing a Monte Carlo Markov Chain algorithm, we compare the predicted orbital motion of S2 with publicly available data and set an upper bound $m_{\psi }\lesssim 3.2\times {10}^{-19}\mathrm{eV}$ on the boson mass, at 95% confidence level. When combined with other galactic and cosmological probes, our constraints help to reduce the allowed range of the bosonic mass to $(2.0\lesssim m_{\psi }\lesssim 32.2)\times {10}^{-20}\mathrm{eV}$, at the 95% confidence level, which opens the way to precision measurements of the mass of the ultralight-bosonic dark matter.

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• Dark matter
• Gravitation
• Particle dark matter
• Axion-like particles