After half a year of work, the Deep Sky Collective is happy to present its latest project - a kilo hour on M31. Not only does this image set new boundaries of what’s possible with collaborative imaging, its release also marks the DSC’s anniversary project! Being launched the 13rd February last year, we never thought we could achieve what we did so far - huge thanks to everyone involved in the DSC and for keeping on believing in what we do.

Behind the scenes we’re working on in-depth tutorials for everyone to access - our hope is that other ambitious photographers out there can make use of these tutorials and get started in collaborative imaging themselves - helping us get started in a new era of collaborative imaging. Expect the first tutorials to be released in 1-2 months.



The Andromeda galaxy, also known as Messier 31, is a galaxy in the constellation Andromeda. It lies at a distance of roughly 2.5 million lightyears, making it the closest (non-satellite) galaxy to our Milky Way. M31 is a big galaxy, spanning some 200.000 ly in diameter whereas our own galaxy “only” spans some 100.000 ly in diameter. Furthermore, M31 is heading towards us at 400.000 km/h which will result in a collision that is predicted to happen in 4.5 billion years - after this collision the two galaxies will merge, forming an even bigger one, set to be named Milkdromeda.
M31 is one of the most popular targets for amateur astrophotographers, as it’s very big in the night sky and very bright, even being visible to the naked eye when observing from dark skies.
In addition to being a fun target for new astrophotographers to go after, M31 also has proven to be worth pursuing for more advanced photographers. This is due to the faint features such as the Halo surrounding M31, the dim Ha background, or the Oiii outbursts, pillar and arc just southeast of the galaxy which was only discovered in 2022 by Drechsler, M. ,Strottner , X. and Sainty Y.
This variety of interesting features made M31 the perfect target for the next Deep Sky Collective project. Having started this target in August, it also marks the longest project we ever had up until now. For this colossal effort, 22 people worked together- 1 Editor, 3 co-editors,  17 photographers and myself, coordinating the project.
Note that the final version is a blend of Uri's and Steeve's edit. 

In our final image of M31 you see here, all of these amazing attributes of M31 can be found - a staggering 488h of Oiii integration was gathered to go as deep as no one managed before. For the Ha emissions in the background, a total of 314h of Ha integration were gathered to provide the deepest look yet. Besides the now traditional H-alpha and Oxygen III for M31, we also decided to do something unusual and get Sii - In the end we ended up with a total of 169h. The goal behind this was to 1) photograph the extragalactic nebulae in M31 in SHO and 2) check for any Sii in the arc - for our findings, refer to interesting features in our image. 
Finally, by Mid January, and after rejecting bad frames we ended up with a record breaking 1056h (or 1 ½ month) of integration over the LRGBHaOiiiSii channels, which marks the longest integration time ever on a single panel for any astrophoto. While the results might diminish at these crazy integration times, the effort more than paid off.

Before we jump into the details of the picture, a big thank you to everyone who played a part in this project. This endeavour is a manifesto to the incredible possibilities that collaborative imaging brings to the amateur community. Working together with all of you has been a real pleasure!








Tim Schaeffer - @Tim Schaeffer
Carl Björk - @Palmito
William Ostling - @William Ostling
Uri Darom - https://astrouri.com/
Steeve Body - https://steevebody.com/


Sébastian Brizé - @Lumotori
Kanwar Brar - @Kanwar Brar
Jasper Capel - @Jasper C
Oliver Carter - @Oliver Carter
Sendhil Chinnasamy - @Sendhil Chinnasamy
Jake Gentillon - @jake_g
Antoine and Dalia Grelin - https://www.galactic-hunter.com
Stephen Guberski - @Stephen Guberski
Charlie Hagen - @Charles Hagen
Richard Hall - @Richard
Florent Herrbach - @Florent Herrbach
Jason Jacks - @jmdl101
Tarun Kottary - @Tarun Kottary
Brian Meyers - @Brian M.
Justin P. - @lokisastro
Kevin Trillsam - @Kevin
Jens Unger - @Jens Unger


Special thanks to:  

• Carl, who put in a tremendous effort - not only did he stack a staggering 5600+ files, but he also developed a whole new stacking workflow with starting help from Charlie, which vastly improves the image quality and allows for automation. Huge thanks for his immense commitment to the project - none of this would be possible without him! Eager to help the community get started with collaborative imaging, he also released the DeepSkyCollective processing suite on PixInsight, containing the newly developed tools that were used for this project. I strongly recommend checking it out on https://elveteek.ch/pixinsight
• William, Uri and Steeve, for their impressive edits. A lot of time and skill goes into these edits, so big thanks! By having multiple edits we could cross check that all details are real.
• Big thank you to Charlie who came up with the new stacking workflow which was later adapted by Carl.
• Sendhil and Tarun, who gave us their excellent Bortle 1/3 data that was kept available for MSGR
• Justin, who provided us with close-up data of the core. As our big stack's core was fried his data was used to blend in and fix the core which was a huge improvement

Notes:

• The final image is a blend of Uri’s and Steeve’s respective edits to create an in depth image in both Broadband and Narrowband. As the two went slightly different ways in editing, Uri emphasising NB while Steeve also brought in more of the BB, the combination of the two images is the perfect mixture for this target.
• The illustrations shown below are mostly using Uri’s edits as he emphasised on NB

Interesting features in our image

• The newly discovered Oiii arc. 

The Oiii arc was discovered in 2022 by Drechsler, M. ; Strottner , X. and Sainty Y. and is one of the most spectacular discoveries of the last few years - this is mainly due to the fact that M31 is the most photographed galaxy and yet no one has ever noticed the Oiii arc up until 2022. The arc itself extends roughly 1.5 x 0.5 degrees and lies 1.2 degrees southeast of M31’s center.
As of right now, our image is one of only a few to show the arc - our goal, and why we chose this target in the first place was to show the true structure of the arc and determine if there is any direct connection between the arc and the “Oiii flower”. As the arc is super faint, different photographs showed varying structures which is a result of pushing the data too far in post processing and enhancing things that are not actual Oiii signal. With our data we concluded that there are likely no stripes of Oiii leading towards the galactic centre and that the arc does have small scale detail (as can be seen when zooming in). Note that saying “there are likely no stripes” we can not be 100% sure - in fact our data does suggest that there is a non-zero chance for there to be a connection towards the galaxy, however this signal is so weak that even with 500h of Oiiii data, we can not tell it apart from the background.
We also paid extra attention in editing as to not push anything that isn’t real signal - for this we have 3 independent edits from 3 different and skilled editors, which all show the same structure.
Photographing the arc was quite hard - as we learned from M51, long sub-exposures are needed to assure that the extremely weak signal doesn’t get lost in the noise. With this in mind we really pushed the individual sub-exposures and ended up with an average exposure of 870”/sub - we believe that this, along with the new stacking method, helped a lot in assuring a strong signal.
As for the origin of the arc, the discovery team has four theories: it could be a galactic supernova remnant, a bright part of an ancient galactic planetary nebula, a result of  violent interactions of stellar and tidal streams due to galactic mergers around M31 or an interaction shock of the galactic halos of the Milky Way with that of M31.
Depending on the real origin, the actual size of the arc can vary from very big to enormous - this however remains a topic of research.
Note that the possible origins explained here are taken from the original discovery team’s paper [1], so if you want a more detailed explanation we suggest checking it out.


©DSC: Blend of Uri’s and Steeve’s edits to show both NB and BB in all its beauty

• Oiii outburst and pillar in M31.

Other amazing features that can (mainly) be found in the Oiii wavelength is the Oiii outburst (also referred to as “Oiii flower”) and Oiii pillar. The outburst, which is proven to lie inside M31 itself,  is thought to be approximately as big as the small magellanic cloud (found in the milky way), making it an enormously huge structure/outburst. What’s fascinating about this structure is that we don’t know for sure what event is energetic enough to cause the ionisation of such a huge structure. One possible explanation would be that it’s a result of interaction with one of its satellite galaxies. The Oiii pillar you see right next to the galactic centre of M31 is also a big structure that stretches several thousands of lightyears and that can be found in M31 itself - it seems as if this pillar rises from the core of the galaxy - there is also some ongoing research regarding this pillar, so it’s nature isn’t well understood yet. 
Below is a picture showing the different structures in detail and different channels. (pretty heavy compression from the GIF)




©DSC: RGB, R and B (from left to right) from Uri's final edit, showing the Oiii flower in all channels

• The faint Hydrogen alpha background. 

First of all, it has to be noted that the Ha you see in this image actually lies in our own galaxy (i.e is Ha cirrus)  and not around M31 as it might seem.
This Ha is also relatively faint and requires a lot of integration time to properly reveal. Here we also went with long sub exposures to ensure that even the faintest signal gets picked up by the sensor - in the end we used 314h of integration in the Ha wavelength. 

©DSC: Uri’s continuum subtracted Ha (left) and the complete red channel (Ha, Sii and R also showing the cirrus)

• Interesting features in Sii. 

As for the Ha, the Sii seen in the background lies within our own galaxy and is Sii cirrus.
The idea to incorporate Sii into our imaging plan came from Carl and we can safely say it was a good idea. Not only does Sii make for a very colourful image in SHO though - in SNRs Sii can be very useful as it shows in regions of strong ionisation, such as bow shocks - the idea here was to shoot Sii and see if there’s any correlations between the Oiii arc and Sii emissions.
We found that there’s a strong correlation between Ha and Sii background structures, which becomes evident when looking at the channels separately (see below).
Furthermore, we believe there could be a correlation between the arc and Sii, as there’s a stripe structure where the arc is - however this can not be said with a lot of certainty and we definitely need a big professional scope to check it out in Sii. Our 169h integration time in Sii doesn’t seem to be enough. Note that this same correlation can be made for Ha and Oiii if you look closely. Previous papers concluded that the Oiii to Ha ratio is greater than 5, but they didn’t conclude that there is no Ha in the arc at all - that being said, we believe this might be a first hint of correlation between Oiii and Ha/Sii in the arc. This is to be taken with a big grain of salt though as it could also just be pure coincidence and not related at all.

©DSC: Continuum subtracted Sii (left) and SHO edit (right) - Uri’s edit

• Many small extragalactic nebulae in SHO. 

As mentioned earlier, we went for not only Ha and Oiii in our image, but also Sii. When combining all that data together, a fantastic and colourful look at M31’s nebula is created. Below you find both a SHO as well as a SHOO close-up edit. Note that the SHOO edit is a natural (i.e true to what our eyes would see) edit and the SHO is used to better visualise where what wavelength is present. As S and H are both red, this valuable information of emission distribution gets lost in a SHOO edit.  


©DSC: Uri’s edit showing all extragalactic nebulae in full detail

• Stars in M31 

Besides all of the immense SNR that enabled us to make out all of the things listed above, the crazy resolution in this project also has to be highlighted - in fact we were able to resolve stars in M31 which is pretty crazy considering how small and far away they are. 



©Photo: Uri's edit, showing amazing details in the galaxy






For any further questions about the project, feel free to leave a comment!

If you want to see our image in greater detail, feel free to go to our website, where the image is uploaded in high resolution ( 6000 x 4159 px), enabling you to explore the picture by yourself and being able to zoom in on every tiny detail!
Link to our website:  https://deepskycollective.com/gallery
While at it, I also recommend checking out the DSC processing suite! 

For this one of a kind kilo-hour project we also decided to produce prints for the first time! If you’re interested in a print, be sure to check out our sale

For a more technical overview of the editing, please refer to Will’s website: coming soon
Finally, Antoine and Dalia made a video talking about this project and you can check it out here: https://www.youtube.com/watch?v=yst7ZOVnSmI&t=576s


Integration overview Here you find a list of integration contribution from all 17 photographers as well as per filter




We hope that you enjoy this image! 
Text written by @Tim Schaeffer  , organiser and co-ordinator of the project and proofread by the team.