And, as @darksapiens.bsky.social points out, the velocity we measure doesn't quite match with the hypothesis presented in this new paper.

Even before us, others published different results (arxiv.org/abs/2303.09425 and arxiv.org/abs/2307.06308).

I think the nebula still remains (a bit) mysterious!

We actually have more evidence supporting that the nebula lies within the Milky Way: For example, the separated [O II] emission we detect with our telescope 🔭 at @cefca-oaj.bsky.social.

You can read a bit more about it in the thread I wrote when we presented the paper: bsky.app/profile/alum...

Great picture! In fact, we already showed last December that this nebula was in the Milky Way, not in Andromeda. Here is the paper: arxiv.org/abs/2412.08327

And here is a thread explaining it:
bsky.app/profile/alum...

It is "slightly" sped up: Roughly one hour from the first to the last frame

Hi! I am the first author of the paper, thank you for sharing!

We used also a telescope from the OAJ (Teruel, Spain). And we are not sure of what it is exactly, but it does seem to be in the Milky Way.

For more info, the paper arxiv.org/abs/2412.08327 and my thread 👇
bsky.app/profile/alum...

Finally, I want to thank all the co-authors and the telescope🔭 operators! Also, thanks to the discoverers of the nebula (Strottner, Dreschler, and Sainty), and thanks to Bray Falls, whose tweet about the discovery I saw and pushed me to start this project!

Ok, it is in the Milky Way... but what kind of nebula is it?

We aren’t sure! It is a complex object, we haven't found anything like it before. It may be a gas filament in our galaxy, with an extra ionization source to explain the [OIII] emission.

More research is needed! 🔭

4. The emission lines are narrow, making it unlikely that the nebula is caused by shock ionization (as proposed if it were near M31), since that requires high velocities and therefore broader lines.

This also suggests it’s probably not a supernova remnant or a planetary nebula.🔭

3. The spectra reveal also emission lines of sulphur, nitrogen, and hydrogen across the nebula. Their velocities and fluxes are similar throughout the object.

This consistency is more typical of smaller nebulae nearby, rather than very distant and large ones.
🔭

2. In the images we obtained with the JAST80 telescope🔭 at the OAJ in Teruel (Spain), we see emission from less ionized oxygen ([OII]), but not in the exact same position as [OIII]!

This is something seen in other nebulae… but only if they are close to us, not if they are as far as M31!

1. The [OIII] we detect in the spectra shows the velocity of the nebula is similar to other objects in our Milky Way, but it differs a lot from M31's velocity.

This suggests it's a regular nebula nearby, not a distant giant one. A bit like a forced perspective trick!
🔭

It has been a stark contrast for me as well! But I think it helps that this paper is not central to our research for any of us, we know we aren't the greatest experts on this topic.
I remember the comments for my first paper and it was brutal as well. I think about it every time I review something!

And if you have any doubt about the data or any idea, feel free to contact me (or @darksapiens.bsky.social, who also works in this project!)