Cosmic Scale
S2
Star orbiting Sagittarius A* · 26,700 light-years
How big is S2?
S2 is about 8,488,000 km across.
S2 is a hot young star orbiting Sagittarius A*, the black hole at the centre of the Milky Way. Following it around its 16-year orbit for three decades proved that something four million times the Sun's mass hides there, and won the 2020 Nobel Prize in Physics.
At a glance
| Diameter | 8,488,000 km |
|---|---|
| Mass | 2.71 × 10³¹ kg |
| Diameter compared with Earth | 666 × Earth |
| Distance | 26,700 light-years |
| Orbit | 16 years |
| Closest approach | 120 times Earth–Sun |
| Top speed | 7,650 km/s |
Good to know
- In 2018 its light was stretched by the black hole's gravity exactly as Einstein predicted.
- Its whole orbit slowly turns with each lap, another effect of relativity, first measured in 2020.
- It is about 14 times the Sun's mass, yet it is whipped around like a pebble on a string.