A Star Dances with Dark Matter Near a Black Hole ⚡ экспресс
Using the motion of star S2 around the black hole Sgr A*, astronomers 'weighed' its dark halo. A new model — a black hole in a cloud of matter with a generalized Dehnen profile — and the Monte Carlo method allowed estimating the parameters: most likely the halo is compact (according to some data, radius less than 0.16 parsecs) and of moderate density. For the first time, such tight constraints on dark matter near a supermassive black hole have been obtained. It's like guessing a fog's shape from the flicker of a distant lantern.
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.