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

Zhao-Qiang ShenGuan-Wen YuanCheng-Zi JiangYue-Lin Sming TsaiQiang YuanYi-Zhong Fan
Mar 2023
Precise measurements of the stellar orbits around Sagittarius A* haveestablished the existence of a supermassive black hole (SMBH) at the Galacticcentre (GC). Due to the interplay between the SMBH and dark matter (DM), the DMdensity profile in the innermost region of the Galaxy, which is crucial for theDM indirect detection, is still an open question. Among the most popular modelsin the literature, the theoretical spike profile proposed by Gondolo and Silk(1999; GS hereafter) is well adopted. In this work, we investigate the DM spikeprofile using updated data from the Keck and VLT telescopes considering thatthe presence of such an extended mass component may affect the orbits of theS-stars in the Galactic center. We examine the radius and slope of thegeneralized NFW spike profile, analyze the Einasto spike, and discuss theinfluence of DM annihilation on the results. Our findings indicate that aninitial slope of $\gamma \gtrsim 0.92$ for the generalized NFW spike profile isruled out at a 95% confidence level. Additionally, the spike radius $R_{\rmsp}$ larger than 21.5 pc is rejected at 95% probability for the Einasto spikewith $\alpha=0.17$, which also contradicts the GS spike model. The constraintswith the VLT/GRAVITY upper limits are also projected. Although the GS NFW spikeis well constrained by the Keck and VLT observation of S2, an NFW spike with aweak annihilation cusp may still be viable, as long as the DM annihilationcross section satisfies $\left< \sigma v \right> \gtrsim 7.7\times10^{-27}~{\rm cm^3\,s^{-1}} (m_{\rm DM}/100~{\rm GeV})$ at 95% level.