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A dance floor where couples whirl. At the center, an invisible master of ceremonies sets the rhythm. This is the supermassive black hole at the heart of the Milky Way, and the couples are stars whose orbits astronomers have tracked for years. But what if the master himself is wrapped in a fluffy fur coat of tenuous matter? That is precisely the possibility the authors of a new study set out to test.

They started with a spacetime model in which a halo of matter, invisible but adding gravity, surrounds the black hole. Two key numbers describe this halo: how dense it is (compactness) and how far it extends (characteristic scale). The scientists then fed these numbers to two independent datasets. The first is the shadow image of the black hole obtained by the Event Horizon Telescope. The second is years of measurements of stellar positions, especially the star S2, which approaches the black hole so closely that it feels every gravitational "breath."

The result was strict. From the shadow alone, one could still allow a fairly dense "fur coat." But the stellar orbits sharply cut the allowed compactness: the matter around the black hole must be extremely fluffy, like a puff of down, not like a felt boot. The characteristic scale, however, remained a mystery — the data fit both a small dense cloud and a large diffuse one equally well.

Thus astronomers turned the Galactic center into a giant scale. The more precisely we know the motion of the dancing stars, the better we sense the invisible partner. Future observations of other stars on wider orbits will help finally understand how matter is distributed around our galactic "conductor."