A team of astronomers has detected the fastest known star in the galaxy. Its extreme velocity stems from a tight orbit around Sagittarius A*, the supermassive black hole at the Milky Way’s center, which holds a mass four million times that of the Sun.
Designated S301, the star reaches 25,000 kilometers per second at peak velocity—roughly 8 percent of the speed of light—and completes an orbit in just 8.7 years. For context, the Sun orbits the galactic center at approximately 230 km/s, making S301 over 100 times faster.
The star’s record-breaking speed is driven by its proximity to the black hole. According to the European Southern Observatory (ESO), S301 passes within a distance comparable to that between Saturn and the Sun at its closest approach. The immense gravitational pull accelerates the star dramatically during this approach, though it avoids capture by following a highly elongated elliptical path.
This orbital geometry explains the drastic velocity shifts. S301 moves fastest at periapsis and slows significantly at its farthest point, mirroring the behavior of comets like Halley’s in our own solar system.
S301 holds the dual distinction of having the highest known orbital velocity in the Milky Way and the closest approach to Sagittarius A*. Researchers suspect the star did not form in its current location and may have once belonged to a binary system.
“S301’s orbital properties, and the fact that stars cannot form so close to a massive black hole, indicate that the star was likely part of a binary pair that was torn apart by the tidal forces of Sagittarius A*,” the ESO explains. “In the process, S301 became trapped by the black hole’s gravity while its companion star was kicked out with high velocity, most likely enough to leave the galaxy altogether.”
Astronomers anticipate that within the next decade they will be able to measure the rotation of Sagittarius A*. Mass and spin are the two fundamental properties defining a black hole; while evidence suggests Sagittarius A* is spinning, its precise rate and orientation remain undetermined.
