A team of amateur astrophotographers, Team New Horizons, has unveiled a comprehensive colour visible light image of the supernova remnant G249.5+24.5, dubbed Hoinga. In December 2023, the team imaged a part of the sky in the constellation Hydra where a “faint possible blob” had been found as part of a search for new celestial objects. Initial imaging revealed unexpected SNR-like filamentary structures, prompting further investigation. The team’s excitement grew as they realised this wasn’t a new discovery, but rather Hoinga, which was first discovered in late 2020 as an X-ray source, and confirmed with data from the Continuum HI Parkes All-Sky Survey (CHIPASS) undertaken with Murriyang, the Parkes 64m radiotelescope. With no detailed published colour images of Hoinga in visible light, the team embarked on a project to create one, unaware that it would evolve into a six-month endeavour.

Hoinga is one of the largest supernova remnants ever discovered in X-rays, with a diameter of about 4.4 degrees – covering an area 76 times that of the full moon in our night sky. Hoinga’s unique characteristics – its large size, distance, and diffuse emission, combine to make it an exceptionally challenging and faint target for astrophotography. Another major challenge was managing the vast dynamic range present in this image. The field contains both very bright small galaxies and ultra-faint filament details that even 80 hours of exposure struggled to capture yet, as shown above, all these challenges were succesfully overcome! More details of how the team put together the final image, which combines OIII, H-alpha, and RGB data, together with a animation of the optical image superimposed on a composite X-ray and radio image, are available from the team’s webpage .