A Star Dances with Dark Matter Near a Black Hole ⚡ экспресс
To study the distribution of dark matter around supermassive black holes, the motion of star S2 was analyzed in the field of a generalized Schwarzschild solution combined with a Dehnen-type halo (1,4,γ) and arbitrary γ. Equations of motion were derived, and the perihelion shift was obtained. Based on two sets of observational data (Do et al., 2019; Gillessen et al., 2017), using MCMC we determined the best-fit parameter values and their 95% upper limits: for the first dataset, γ = 1.18^{+1.03}_{-0.81}, ρ_s = 0.37^{+0.42}_{-0.29}, r_s = 0.05^{+0.05}_{-0.03} with upper boundaries γ<2.66, ρ_s<0.93, r_s<0.16; for the second, γ=1.23^{+1.01}_{-0.85}, ρ_s=0.31^{+0.44}_{-0.26}, r_s=0.14^{+0.18}_{-0.10} with constraints γ<2.67, ρ_s<0.92, r_s<0.52. The results show that precise measurements of stellar orbits can impose significant constraints on dark matter profiles in galactic nuclei and shed light on the environment of Sgr A*.
At the heart of our stellar metropolis — the Galaxy — lurks the supermassive black hole Sagittarius A*. Around it, star S2 whirls in a swift dance. But its movements reveal more than just the hole's pull: an invisible partner joins the dance — dark matter. Back in the 1970s, Vera Rubin showed that galaxies would fly apart without it, yet its distribution near black holes remained a puzzle.
Astronomers applied a flexible mathematical model, built on Schwarzschild's equations, to years of S2 observations. They didn't need to predefine the shape of the invisible cloud — the model deduced it from slight wobbles in the star's "dance." This made it possible for the first time to pin down how much dark matter can accumulate in a black hole's vicinity.
Most unexpectedly, these mere fractions of a percent of trajectory distortion, accumulated over several orbits, sufficed to "weigh" the invisible. Without dark matter, S2 would have exited the stage long ago, and we'd have never known about this unseen choreographer. Understanding such subtle gravitational choreography offers a key to how dark matter orchestrates the growth of the entire Galaxy. In essence, spacetime curvature — the very dance floor on which the dancers glide — revealed the dark partner.
🎯 The black hole Sagittarius A* is 4 million times more massive than the Sun, yet squeezed into a region smaller than Mercury's orbit.