Sagittarius A*
What is Sagittarius A*?
Black holes & quasars· Distance ~26,000 ly. The supermassive black hole at our galaxy's heart — betrayed by stars whipping around an invisible point, and imaged directly by the EHT in 2022.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where Sagittarius A* is in your sky right now: https://nowsky.org/solar/sky?sel=sgr a — location and time set automatically, no login.
Its place in the sky
A black hole, in the direction of Scorpius.
Mass, distance, nature
| Distance | ~26,000 ly |
|---|---|
| Mass | 4.3 million solar masses |
| What | our galaxy's central black hole |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Discovery and name
A radio source found in 1974. Thirty years of tracking stars orbiting it revealed a 4-million-Sun black hole (Nobel 2020).
Frequently asked
- How far is Sagittarius A* from Earth?
- ~26,000 ly.
- What is the mass of Sagittarius A*?
- 4.3 million solar masses.
- What kind of object is Sagittarius A*?
- our galaxy's central black hole.
- Where in the sky is Sagittarius A*?
- In the direction of Scorpius.
- Where is Sagittarius A* in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
A shadow that changes by the minute — five years for one picture
The image of Sagittarius A* came three years after M87*'s, though both were observed in the same April 2017 campaign. The delay was a matter of size. M87* is so large that gas takes days to circle it and it sits still through a night's observing, but Sagittarius A* is 1,500 times smaller and its gas orbits in minutes — like photographing a moving subject with the shutter held open, so recovering the ring from the blurred data required cross-checking several methods.
The result, released in May 2022, gave a ring whose size matched the mass computed from stellar orbits (4.3 million Suns) and the prediction of general relativity. The dust hiding the galactic centre is transparent to radio waves, which made the observation possible, but the blurring from Earth's atmosphere and from interstellar plasma had to be removed separately. That the two black holes show the same ring shape means the physics around a black hole is the same whether its mass differs by a factor of 1,500 or not.
The black hole in depth
At the Milky Way's heart sits Sagittarius A*, a black hole of 4.3 million solar masses. The clincher was stellar motion: for decades astronomers tracked star S2 whipping around "something unseen" at about 27.5 million km/h (2.5% of light speed) on a 16-year orbit — work that won the 2020 Nobel Prize in Physics.
In 2022 the Event Horizon Telescope, an Earth-sized network of radio dishes, imaged its shadow directly: darkness ringed by lensed light, exactly as general relativity draws it.
The solar system orbits this center once every 230 million years — dinosaurs were new the last time around. Find the galactic-center marker toward Sagittarius in the Sky view; it lies 26,000 light-years ahead.
The black hole's mass was weighed with stellar orbits — above all S2, a star that whips past at 2.5% of light speed (about 7,650 km/s) every 16 years; the decades-long tracking earned two teams the 2020 Nobel Prize. When the Event Horizon Telescope unveiled its ring image in 2022, the size matched those orbital calculations exactly — an invisible object confirmed two independent ways.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.