M31 reveals a secret

Probably one of the most observed and photographed objects in the night sky has recently revealed a secret unknown before. A group of amateur astrophotographers has imaged M31 in OIII and discovered a massive arc-shaped cloud hanging over the galaxy, emitting in the OIII bandwidth.

In total 111h of exposure was required to show the galaxy with its newly discovered feature in all its beauty. Continuüm Subtraction with Blue helped to get the maximum amount of detail out of 45h of OIII exposure. The result is as beautiful as it is astonishing. All this time this has been under our noses. But it took a group of astrophotographers to discover it and share it with the world.

Marcel Drechsler, Xavier Strottner, Yann Sainty, Bray Falls and several others have been collaborating to achieve this exciting result. The image, its contributors and all the details can be found on Astrobin. There is also YouTube channel where the discovery is presented. The video is available in three languages.

This is one discovery in a whole series of discoveries of OIII objects, which are collectively known as the Strottner-Drechsler (StDr) catalogue.