Cosmic Scale
Sagittarius A*
Supermassive black hole · 26,700 light-years
How big is Sagittarius A*?
Sagittarius A* is about 2.5 × 10⁷ km across.
See Sagittarius A* in 3D, at true scale
Sagittarius A* is the supermassive black hole at the centre of the Milky Way, 26,700 light-years away. We knew it was there long before we saw it, because we could watch stars whipping around something invisible and enormously heavy.
At a glance
| Diameter | 2.5 × 10⁷ km |
|---|---|
| Mass | 8.55 × 10³⁶ kg |
| Diameter compared with Earth | 1,990 × Earth |
| Distance | 26,700 light-years |
| Imaged | 2022, Event Horizon Telescope |
| Nobel Prize | 2020 |
Good to know
- The star S301 whips around it every 8.7 years at over 8% of the speed of light, the fastest star known.
- Tracking those stars for decades won Reinhard Genzel and Andrea Ghez the Nobel Prize in Physics.
- It is quiet as black holes go, swallowing only a trickle of gas.