Constraining ultralight bosonic dark matter with Keck observations of S2's orbit and kinematics

TL;DR

This study uses precise orbital data of the S2 star around Sgr A* to set new constraints on ultralight bosonic dark matter clouds, testing their gravitational and coupling effects with improved observational limits.

Contribution

It provides the first detailed analysis of S2 star data to constrain scalar dark matter clouds and their interactions with ordinary matter, including Higgs and photon portals.

Findings

Established upper limits on scalar cloud mass and coupling strength.

Most stringent constraints for scalar masses between 3.2×10⁻¹⁹ eV and 1.6×10⁻¹⁸ eV.

Data consistent with a point-like mass of Sgr A*.

Abstract

Ultralight bosonic dark matter is expected to be able to form a cloud surrounding the supermassive black hole (SMBH) in the Galactic center. With increasing precision of the observations of the stellar kinematics around the SMBH, tiny effects from such a dark matter cloud, including its gravitational perturbation and the direct coupling with the ordinary matter may be detectable. In this work, we search for possible evidence of the scalar cloud using accurate orbital measurements of the S2 star around Sgr~A*. We solve the first order Post-Newtonian equation, considering simultaneously the extended mass distribution of the scalar cloud and the frequency shift induced by the additional coupling via Higgs portal or photon portal interaction. Furthermore, we also investigate the impact of an astrophysical power-law component from the gas and stellar remnants. We find that the astrometric and spectroscopic data of the S2 star are well consistent with the scenario of a point-like mass of Sgr~A*. We thus derive upper limits of the coupling of the new interaction and the extended mass, with and without the contribution from the astrophysical component. The limits of the Higgs/photon coupling and the extended mass of the scalar cloud are the most stringent ones for the scalar mass window between $3.2\times 10^{-19}$~eV and $1.6\times 10^{-18}$~eV.