New star S301 completes an 8.7-year orbit around Sagittarius A*, edging toward measuring the Milky Way's black hole spin

Astronomers using GRAVITY+ have identified S301, a faint star on an 8.7-year orbit around the Milky Way’s central black hole Sagittarius A*, passing within about 136–142 Schwarzschild radii at roughly 25,000 km/s (≈8% of light). The current data cannot yet measure the black hole’s spin, and the orbit has two mirror solutions due to the lack of radial velocity. Forecasts show that with improved astrometry and spectroscopy—potentially by 2035–2036 under optimistic conditions—a spin constraint could be detected with high significance, though a robust result will require more data and second post-Newtonian modelling.