ESO astronomers discover fastest known Milky Way star, S301, orbiting Sagittarius A*
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ESO astronomers discover the fastest known star in the Milky Way, S301, orbiting the supermassive black hole Sagittarius A*. The star reaches 25,000 km/s at closest approach and completes an orbit in 8.7 years. Its orbit gives scientists the first direct opportunity to measure the black hole's spin.
Key Facts
- European Southern Observatory astronomers identified S301 using the Very Large Telescope Interferometer and the GRAVITY+ instrument.
- S301 orbits Sagittarius A*, the supermassive black hole at the center of the Milky Way, with a period of 8.7 years.
- The star reaches 25,000 km/s at closest approach, about 8% of the speed of light, making it the fastest stellar object observed in the Milky Way.
- S301 passes within about 1.78 billion km of Sagittarius A*, roughly 12 times the Earth-Sun distance and comparable to the Sun-Saturn distance.
- Astrophysicists hypothesize that S301 was once part of a binary system whose companion was ejected from the galaxy while S301 was captured by the black hole.
Discovery of S301
European Southern Observatory astronomers used the Very Large Telescope Interferometer and the GRAVITY+ instrument to detect the star designated S301. S301 orbits Sagittarius A*, the supermassive black hole at the center of the Milky Way. The star completes one full orbit in 8.7 years and reaches 25,000 km/s at maximum approach. This speed is about 8% of the speed of light and makes S301 the fastest stellar object ever observed in the Milky Way. The star approaches the black hole to within about 1.78 billion km, or 12 times the Earth-Sun distance, comparable to the distance from the Sun to Saturn.
Binary Origin and Spin Measurement
Astrophysicists hypothesize that S301 was once a member of a binary star system. Tidal forces near the black hole tore the system apart, ejecting the second star from the galaxy at hypervelocity. S301 remained bound and was captured by Sagittarius A*'s gravity. The star's extreme proximity offers the first direct opportunity to measure the spin of Sagittarius A*. Under general relativity, a rotating black hole drags spacetime and shifts the orbits of nearby objects.
2031 Relativity Test
S301 will make its next close approach to Sagittarius A* in 2031. Monitoring the star over the next decade will allow scientists to record the predicted orbital shift. The measurements are intended to experimentally test predictions of general relativity.
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ESO astronomers discover fastest known Milky Way star, S301, orbiting Sagittarius A*
