Probing Dark Matter Interactions with Stellar Motion near Sagittarius A*

Abstract

Stars orbiting Sgr A* at the Milky Way's center provide a unique laboratory to test gravity and dark matter (DM). We demonstrate that DM interactions in stellar interiors induce a novel momentum transfer force, altering orbits beyond gravitational effects. Using S2's 2000-2019 orbital data we derive the first astrophysical constraints on DM-nucleon scattering, excluding new sub-GeV parameter space. Stellar lifetime constraints over Myr timescales complement these, surpassing some direct detection and cosmological limits. This establishes stellar dynamics as a novel probe of DM interactions.

Figures (6)

• Figure 1: Left: RV deviations induced by DM obtained from our simulations. Dashed lines indicate the difference between a stellar orbit without a DM overdensity spike and one with a spike and only gravitational interactions. Solid lines indicate the difference between two orbits with DM spikes with and without DM-nucleon scattering. We consider a characteristic DM spike profile with $\gamma = 7/3$, $\rho(0.01 \mathrm{pc}) = 10^{10}~\mathrm{GeV ~cm^{-3}}$ as well as $\tau_{T} \gg 1$ for DM scattering. The dotted horizontal line indicates the reach of 10 km s$^{-1}$ for near future astrometric measurements S2OrbitDataGRAVITY-AstrometricAstrometry30MTNIFS-ParametersOsiris-Resolution. Right: DM density at 0.01 pc versus spike index for $m_{\chi} = 10^{-2}$ GeV and $\sigma_n = 5 \times 10^{-35}~ \mathrm{cm^{2}}$ with a heavy mediator. Solid lines denote tidal disruption events within 1 Myr, the purple shaded region indicates parameters where any of the four stars would undergo a tidal disruption. Dashed lines correspond to observational sensitivities of 10 km s$^{-1}$ or 0.1 mas. The red region denotes where DM scattering effects on S2 in 2000-2019 data cause deviations exceeding measurement uncertainties S2OrbitData. The 1-$\sigma$ and 3-$\sigma$ gravitational only exclusions from GRAVITY GRAVITY:2024tth are shown. The black star indicates the parameters used in Fig. \ref{['fig:sigma']}.
• Figure 2: DM-nucleon scattering cross-section versus DM mass for a heavy mediator (left) and a light mediator with $m_V = 1$ eV (right). A characteristic DM overdensity spike index of $\gamma = 7/3$ and density $\rho(0.01 \mathrm{pc}) = 10^{10}~\mathrm{GeV ~cm^{-3}}$ is considered. The red region denotes where DM scattering effects on S2 in 2000-2019 data cause deviations exceeding measurement uncertainties S2OrbitData. Solid lines mark tidal disruption events within 1 Myr, the purple region indicating parameters where any of the four stars would undergo a tidal disruption. Dashed lines correspond to deviations of 10 km s$^{-1}$ in RV or 100 $\mu$as in RA or Dec over 20 yr period, comparable to current and near future sensitivities S2OrbitDataGRAVITY-AstrometricAstrometry30MTNIFS-ParametersOsiris-Resolution. Limits from direct detection from SENSEI, XENON, LUX, and PandaX SENSEI:2020dpaSENSEI:2023zdfMigdal2019LUX:2018akbPandaX-II:2018xpz as well as cosmological constraints Buen-Abad:2021mvc that include CMB with BAO, Lyman-$\alpha$ forest and Milky Way satellite measurements are shown. We also display cosmic-ray boosted DM bound estimates for IceCube Cappiello:2024acu and limits from Super-Kamiokande Super-Kamiokande:2022ncz, indicated with hatched contours and dashed lines reflecting their additional model dependence and complementarity. The black star in the left panel marks parameters used in Fig. \ref{['fig-Direct-Observables']}.
• Figure 3: Same as the left panel of Fig. \ref{['fig-Direct-Observables']}, but showing the differences in RA (left) and Dec (right). A characteristic DM overdensity spike index of $\gamma = 7/3$ and density $\rho(0.01 \mathrm{pc}) = 10^{10}~\mathrm{GeV ~cm^{-3}}$ is considered. Dashed lines denote purely gravitational effects, while solid lines include DM induced scattering.
• Figure 4: Left: Graph of the gravitational (dashed line) and scattering induced effects (solid line) on S2 radial velocity between 2000 and 2019. The horizontal line is the average uncertainty on the radial velocity measurements during this time from S2OrbitData. Right: Range of the stellar radii as a function of time considering the energy loss due to scattering of DM within the spike. A characteristic DM overdensity spike index of $\gamma = 7/3$ and density $\rho(0.01 \mathrm{pc}) = 10^{10}~\mathrm{GeV ~cm^{-3}}$ is considered. Solid lines indicate the apocenter distance, while dashed lines indicate the pericenter distance.
• Figure 5: Dominant contribution to the orbital evolution of the semimajor axis $a$ and eccentricity $e$, as a function of $a$ and $e$, comparing DM scattering, gravitational wave (GW) emission and dynamical friction (DF). We consider DM with a mass $m_{\chi} = 10^{-2}$ GeV with a cross section of $\sigma_n = 1.37 \times 10^{-36}~\mathrm{cm^2}$. A characteristic DM overdensity spike index of $\gamma = 7/3$ and density $\rho(0.01 \mathrm{pc}) = 10^{10}~\mathrm{GeV ~cm^{-3}}$ is considered. For this comparison we consider a star with solar mass and radius. The locations of the four S-cluster stars analyzed in this work are also indicated.