Astronomers find S301, fastest star near Sagittarius A*
This digest was compiled by AI from multiple sources — links to the originals are below.
Astronomers using the European Southern Observatory’s GRAVITY instrument identify S301, a star that orbits Sagittarius A* every 8.7 years, the shortest known period near the Milky Way’s central black hole. The star reaches about 90 million km/h, more than 8% of the speed of light, and passes within 11.5 astronomical units of the black hole, giving researchers a new probe of its spin.
Key Facts
- S301 orbits Sagittarius A* every 8.7 years, more than three years shorter than any other known star near the black hole.
- The star reaches about 90 million km/h — more than 8% of the speed of light — the fastest recorded speed for any star.
- S301's closest approach to Sagittarius A* is 11.5 astronomical units, somewhat farther than Saturn's orbital distance from the Sun.
- S301 is about 50% more massive and five times brighter than the Sun.
- The discovery was reported on Aug. 19 in Nature.
GRAVITY Instrument Observations
The European Southern Observatory’s GRAVITY instrument on the Very Large Telescope combines light from four individual telescopes, achieving the resolution of a 130-meter telescope. Since 2017, the GRAVITY team has tracked stars in the immediate vicinity of Sagittarius A*, converting interferometric data into images. In 2023, the team spotted a star moving away from the black hole and named it S301. After several months of observations, they estimated its orbit and confirmed the object in earlier data.
Orbital Parameters
S301 completes one orbit around Sagittarius A* every 8.7 years, more than three years shorter than any other known star in the region. The orbit is highly elliptical, with an eccentricity of 0.9832, close to the escape threshold of 1. The star reaches speeds up to 90 million km/h, exceeding 8% of the speed of light. Its closest approach to the black hole is about 11.5 astronomical units, somewhat farther than Saturn's orbital distance from the Sun. S301 is about 50% more massive and five times brighter than the Sun.
Black Hole Spin Measurement
Sagittarius A* is a supermassive black hole with a mass of 4.3 million solar masses. S301's tight orbit brings it close enough that its orbital precession should reveal the black hole's spin. Researchers expect to measure the black hole's spin within about a decade using S301's motion. No other star has been clocked at this speed, making S301 a unique probe of the galactic center.
4 sources
Astronomers find S301, fastest star near Sagittarius A*
