The Andromeda galaxy, one of the closest and best-known companions of our own galaxy, has been hiding from the astronomers' eyes one of its secrets: although it has always been considered as a typical spiral galaxy, it has now been shown to be a spectacular ringed galaxy.
"Observations such as the ringed skeleton of Andromeda confirm that ISO is unveiling a totally new face of the Universe, with its unique ability to peer into regions never seen before. ISO is making the invisible visible," said Martin Kessler, ISO Project Scientist.
Andromeda, at only two million light-years away, is a very well known galaxy, also called M31. But when observed in the infrared, what optical telescopes interpret as a big galaxy typically spiral-shaped, turns out to be structured in multiple concentric rings.
Moreover, a large fraction of the dust and most of the gas of the galaxy - roughly the same size as our own, the Milky Way - gathers in just one ring, the brightest. Many new stars are being born in this ring, which has a radius of 10 kiloparsec (30 000 light years, about the same distance as between the Solar System and the centre of our own galaxy, the Milky Way).