Sagittarius A* - the black hole at the centre of the Milky Way

node · earth · Galactic centre, constellation Sagittarius as seen from Earth

The compact radio source at the dynamical centre of our own galaxy, about 8.3 kiloparsecs away, whose mass of roughly four million solar masses is known more securely than that of any other black hole because individual stars have been tracked around it for three decades. The Event Horizon Telescope published an image on 12 May 2022 showing a ring about 51.8 microarcseconds across, in close agreement with the size the stellar-orbit mass predicts - two entirely independent methods, one Newtonian celestial mechanics applied to stars, one general-relativistic light bending, converging on the same object. It was much harder to image than M87* despite being far closer, because its far smaller mass means the material orbits in minutes rather than days, so the source changes during the observation. Getting an image at all required averaging over many reconstructions and treating the variability explicitly. It is also extremely faint for its mass, accreting at a tiny fraction of the Eddington rate. Not a place on Earth.