Exploring dark matter spike distribution around the Galactic centre with stellar orbits

Abstract

ABSTRACT Precise measurements of the stellar orbits around Sagittarius A* have established the existence of a supermassive black hole (SMBH) at the Galactic centre (GC). Due to the interplay between the SMBH and dark matter (DM), the DM density profile in the innermost region of the Galaxy, which is crucial for the DM indirect detection, is still an open question. Among the most popular models in the literature, the theoretical spike profile proposed by Gondolo & Silk (GS hereafter) is well adopted. In this work, we investigate the DM spike profile using updated data from the Keck and Very Large Telescope (VLT) telescopes considering that the presence of such an extended mass component may affect the orbits of the S-stars in the GC. We examine the radius and slope of the generalized Navarro–Frenk–White (NFW) spike profile, analyse the Einasto spike, and discuss the influence of DM annihilation on the results. Our findings indicate that an initial slope of γ ≳ 0.92 for the generalized NFW spike profile is ruled out at a 95 per cent confidence level. Additionally, the spike radius Rsp larger than 21.5 pc is rejected at 95 per cent probability for the Einasto spike with α = 0.17, which also contradicts the GS spike model. The constraints with the VLT/GRAVITY upper limits are also projected. Although the GS NFW spike is well constrained by the Keck and VLT observation of S2, an NFW spike with a weak annihilation cusp may still be viable, as long as the DM annihilation cross-section satisfies $\left\langle \sigma v \right\rangle \gtrsim 7.7\times 10^{-27}~{\rm cm^3\, s^{-1}} (m_{\rm DM}/100~{\rm GeV})$ at 95 per cent level.