Sagittarius A*

Sagittarius A* is the supermassive black hole at the centre of our Milky Way. It has about 4.3 million solar masses and lies roughly 26,700 light-years away. Its event horizon is about 25 million kilometres across, around 18 Sun diameters.

Stars such as S2 orbit it in only about 16 years. Measuring these orbits earned the 2020 Nobel Prize in Physics (Reinhard Genzel and Andrea Ghez, shared with Roger Penrose).

In May 2022 the Event Horizon Telescope collaboration published the first image of this black hole. It shows the glowing ring of hot gas around the dark shadow – the hole itself cannot be seen.

In visible light the Galactic Centre is hidden behind dense dust clouds. It is observed in infrared, radio waves and X-rays. In the sky it lies in the constellation Sagittarius.