At the center of our Galaxy lies a supermassive black hole, with stars orbiting around it. Their motion resembles a cosmic dance: some race along elongated orbits, others follow nearly circular paths. If invisible dark matter exists near the black hole, it slightly distorts these orbits, like an unseen hand nudging a star off course.
The authors calculated how different dark matter distribution profiles affect the shift of the closest point of an orbit to the black hole — the pericenter. For star S2, which completes an orbit in 16 years, the effect turned out to be negligible: its orbit is too close to the black hole, whose gravity completely dominates. However, stars with wider and less elongated orbits feel dark matter more noticeably. Their pericenter shifts by microscopic fractions of an arcsecond — roughly the thickness of a human hair seen from a thousand kilometers away.
Current instruments are already capable of detecting such shifts. The GRAVITY instrument on the Very Large Telescope and the future Thirty Meter Telescope (TMT) will not only notice the effect but also distinguish between different dark matter profiles. This matters because the distribution of dark matter at the Galactic center tells us how our stellar system formed billions of years ago.
At its closest approach to the black hole, star S2 accelerates to 7650 kilometers per second—2.5% of the speed of light. Even at such speed, dark matter barely affects its orbit.
In Dan Simmons's novel 'Hyperion,' the black hole at the Galactic center serves as a portal — here, the stars around it act as detectors of invisible matter.