So I was talking about the recent discovery in 2023 of the giant Oxygen III Arc neighboring Andromeda. It is arguably the biggest discovery of 2023 in astronomy (not cosmology), because it is the closest giant structure (magellanic cloud sized) that was hidden in plain sight. The Arc is gorgeous and its nature is intriguing, but the most groundbreaking aspect of the discovery, is not the discovery itself, but the meta discovery that there are entire aspects of the universe we have not imaged and those can yield considerable discoveries. I could digress about the prospects of specific wavelengths ranges that are currently being sadly ignored (e.g UV astronomy, sub millimeter), or about gaps in transient astronomy or in polarimetry but here the topic is about spectroscopic imaging of specific atomic emission lines. It has only recently become possible to have high resolution spectrographs that have a “large” field of view and indeed many observations of hydrogen lines are revealing gas structure. However there are a few other emission lines that have major prospects to image things we couldn’t see before, mainly, CO, CII and OIII. While I can’t speak as to the status of the two formers, the discovery of Andromeda giant blue arc by amateurs was due to the concomitance of the very recent democratization of wide field spectrographs and the fact they did very long exposure time, which is necessary for such faint objects.
If there was such a gigantic object so close to us, one might wonder whether gas structure emitting faint OIII are widespread and indeed this is the revolutionary discovery I previously missed, researched imaged multiple nebulaes in OIII and they found OII gas structure/filaments in all of them, not only that but the structure being revealed, are for the most part non redundant/overlapping with hydrogen and in many cases are invisible to all other wavelengths! (I don’t get which mechanism would allow such frequency selectivity) It is like half of the picture of the real morphology of nebulaes was finally shown to use, I’m sure this will allow many inferences in astrophysics but in the meantime those are absolutely gorgeous and the number of imaged nebulaes in OIII should explode after such results, look for example, at figure 36! It is unprecedented and a new chapter for astronomy. (note: every blue pixels in the images are new discoveries)