Dark Drag Around Sagittarius A*

TL;DR

This work demonstrates that non-gravitational dark matter–Standard Model interactions near the Galactic Center can generate a dissipative drag on orbiting bodies, potentially causing rapid orbital decay. By formulating a dark-drag framework in the free molecular flow limit and applying it to DM density profiles (including spikes) and GC objects, the authors derive cross-section constraints across a wide DM-mass range, notably from the gas cloud G2 and, to a lesser extent, the S-stars. The results show complementary constraints to direct detection and cosmology, with sub-GeV and inelastic MeV-scale splittings being accessible, and even ultralight DM effects becoming testable via coherence enhancements. Additionally, the paper explores how dark drag could contribute to the observed paucity of red giants near the GC, suggesting a novel astrophysical channel to probe DM–SM portals and outlining future observational and theoretical avenues.

Abstract

We analyze the effect of Dark Matter (DM) - Standard Model (SM) non-gravitational interactions on the orbital dynamics of celestial bodies near the supermassive black hole Sagittarius A*, where the DM density is generically expected to be high. We outline the conditions under which a DM-SM scattering channel gives rise to a drag force on objects in this region, and show that for sufficiently large cross-sections, this effect can lead to observable orbital decay on timescales as short as a single orbital period. We identify the types of objects most strongly affected by this dark drag and place constraints on specific dark matter distributions and interaction strengths, assuming both elastic and inelastic scattering. For inelastic DM, we find sensitivity to mass splittings that reach the MeV scale. We also demonstrate that a DM-induced drag force could potentially contribute to the observed depletion of red giant branch stars in the innermost region of the Milky Way.

Figures (8)

• Figure 1: Various dark matter density profiles considered in this work. Lines labeled as NFW and gNFW correspond to Eq. \ref{['eq: nfw density']} with slopes of $\gamma = 1$ and $\gamma = 1.5$ respectively. Lines labeled by their spike index $\gamma_{\rm sp}$ correspond to DM spikes which grow on top of an NFW profile with a spike radius of $R_{\rm sp}=1$ pc (see text). Burkert and Einasto refer to the cored profiles defined by Eqs. \ref{['eq: Burkert']} and \ref{['eq: Einasto']}. The vertical dashed line corresponds to $r=131.5$ AU, the distance of gas cloud G2's last pericenter passage for reference gillessen2012gas. The gray horizontal lines show $\rho^{\rm (max)}_\chi$ for symmetric DM with various masses and annihilation cross-sections.
• Figure 2: The blue shaded region corresponds to excluded DM-SM cross sections based on G2's orbital decay after its most recent pericenter passage. These lines apply to dark matter in the mass range 1 eV $\lesssim m_\chi \lesssim$ 1 GeV for nucleon scattering, and 1 eV $\lesssim m_\chi \lesssim$ 0.5 MeV for electron scattering. Vertical lines correspond to benchmark DM density profiles which give rise to the densities shown at G2's pericenter distance $r_p = 131.5$ AU (see Fig. \ref{['fig: density profiles']}).
• Figure 3: Excluded DM-electron cross section based on G2's orbital decay for various DM distributions as specified. Additional limits from FIRAS Ali-Haimoud:2015pwa, CMB+BAO measurements Buen-Abad:2021mvc, LeoT cooling Wadekar:2019mpc, direct detection Hochberg:2021yudEssig:2012yxDarkSide:2022knjSENSEI:2020dpa are shown. The vertical dashed line approximately indicates the Tremaine-Gunn limit for light fermionic DM Tremaine:1979we. Possible additional constraints are discussed in the text.
• Figure 4: Same as Fig. \ref{['fig: electron sensitivity eV - GeV']} for DM-nucleon cross section. Additional limits from the X-ray Quantum Calorimeter Erickcek:2007jv, L1551 gas cloud ionization Blanco:2023bgz (see also Bhoonah:2018gjbBhoonah:2018wmw), Milky Way satellites 2021PhRvL.126i1101N, as well as cosmological bounds derived from CMB Boddy:2022tytGluscevic:2017ywp and Lyman-$\alpha$ observations Rogers:2021byl. Possible additional constraints are discussed in the text.
• Figure 5: Same as Fig. \ref{['fig: nucleon sensitivity eV - GeV']}, except for ultralight masses where coherence greatly enhances cross section sensitivity. We also show the associated constraints from MICROSCOPE as discussed in the text MICROSCOPEcollabBanerjee:2022sqg.