A galaxy is like a cosmic highway where stars, like cars, race along circular orbits. Their speed is set by the invisible "cargo" of mass enclosed within the orbit: the more massive the central region, the faster the stars at the periphery. Back in the 1970s, Vera Rubin spotted an anomaly: at the edges of galaxies, the rotation speed remained suspiciously high, as if someone had invisibly "tweaked" gravity. The natural explanation was the presence of invisible extra mass — dark matter, a hypothetical substance that neither emits nor absorbs light but reveals itself through gravitational interaction. However, some researchers took a different path, suggesting that the issue wasn't hidden mass but the need to modify the very laws of gravity.

New observational data from the Gaia space telescope have allowed us to look at the problem from an unexpected angle. It turns out that stars in the galactic disk don't just rotate: they also undergo vertical oscillations, "bobbing" up and down relative to the disk plane. This three-dimensional motion became an ideal testing ground for theories. Scientists tested two leading versions of modified gravity — MOND (Modified Newtonian Dynamics) and STVG (Scalar-Tensor-Vector Gravity). Neither could simultaneously reproduce both the circular "race" of stars and their vertical "jitter." In contrast, the model that includes dark matter as a massive invisible halo enveloping the galaxy handled both tasks flawlessly. The statistical significance of the differences was colossal: for MOND, the discrepancy with observations reached 13 sigma — roughly like tossing a fair coin and getting heads a hundred times in a row; for STVG, 4 sigma. Thus, Einstein's curvature of spacetime, amplified by the gravitational contribution of dark matter, passed the double test. Stellar kinematics left no doubt: you can't fool gravity, and the stars have clearly pointed to the true conductor of their motion.