S301

Common card · No. 313197

S301 is a faint main-sequence star orbiting Sagittarius A* (Sgr A*), the supermassive black hole at the centre of the Milky Way. Its discovery was reported by the GRAVITY collaboration in August 2026. At its closest approach to the black hole, S301 reaches a speed of about 25,000 km/s (16,000 mi/s), more than 8% of the speed of light, making it the fastest known star in the Milky Way at the time of its discovery. S301 follows a highly eccentric orbit with a period of about 8.7 years, the shortest securely established orbital period of any star around Sagittarius A*. At pericentre, it approaches to about 12 astronomical units (AU) from the black hole, roughly comparable to the distance between the Sun and Saturn (it exceeds Saturn's average orbital radius by only 24%). Its close orbit makes S301 a potentially important probe of general relativity, and continued observations could enable the first direct measurement of the spin of Sagittarius A*.

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