The doughtnut around a black hole
Ingenious research finally reveals the true shape of the Milky Way.
April was quite a month for out-of-thisworld photos from space. Just days before NASA released the first direct image of a black hole (see page 35), astronomers led by Chris Carilli, of the National Radio Astronomy Observatory in Virginia, unveiled a coup of their own.
The blue-to-green oval in the centre of this image is a thick, dusty “doughnut” surrounding a rotating disk of material that is itself falling into the maw of a supermassive black hole that lies at the centre of Cygnus A, a galaxy 760 million light-years from Earth.
It’s a phenomenon long theorised, but never before directly seen.
All black holes, astronomers conclude, are surrounded by a ring of infalling material, and spew outflowing jets.
This set of features is called the active galactic nucleus (AGN).
However, black holes in different parts of the universe, and set at different angles of view to terrestrial or orbiting telescopes, don’t all look the same – a condition that led to them being divided into categories, such as quasars, blazars, or Seyfert galaxies.
The AGN model works on the assumption that such divisions represent a false taxonomy. To explain this, the notion of the torus was introduced.
All black hole-powered “central engines” are basically similar (except in the matter of mass), the theory runs, but the torus is massive and thick, and obscures whatever is behind or inside it, relative to an observer, altering their appearance.
Now, however, Carilli and colleagues have succeeded in directly observing one for the first time.