Leaving the Milky Way behind: galaxies far, far away

"Space is big. Really big. You just won’t believe how vastly hugely mindbogglingly big it is." [i]

This is the fourth and final image-rich post in a series within which I hope to share my progress in astrophotography; the first is here, the second is here and the third here. I decided to write these posts as a means of taking stock of what I’ve achieved in the years since taking up this challenging hobby in my mid-60s. There’s nothing like writing about something to sort out one’s thoughts. The 'backstory' to this current short series may be found spread through several earlier posts: they'll be obvious if you peruse the blog. An alternative to reading those would be to watch a recording of the talk I gave in January 2025 which summarises the earlier stages of my journey: there’s a link to the YouTube capture in the first paragraph of ‘Climbing over Failure’. Following the pattern of my first three posts in this series, what follows is a collection of my images; the captions will provide additional information. Their quality varies simply because my equipment, software and associated proficiency and skill have evolved over time.

The type of astronomical target I’ll introduce here are galaxies: edge-on, face-on, elliptical, spiral – barred or unbarred – and lenticular; large, small and dwarf; near-neighbours and far-flung; isolated or clustered. The variety is impressive, but not as impressive as their sheer beauty. I’m still awed by the fact that modern amateur equipment is able to reveal these giant but exceptionally faint objects from my garden, even in the presence of light pollution. Trillions upon trillions of stars illuminating the universe. Thus far, we have covered distances ranging from a few tens of light-years (ly) through to a thousand light-years or so as we’ve considered binary star systems, star clusters and nebulæ. Now we must talk in terms of millions – even hundreds of millions – of light-years. The light from the more distant galaxies shown in the images below began its journey to my garden near the start of the Mesozoic Era, during which dinosaurs appeared and moved through forests of early conifers, and the ancient continent of Pangaea was breaking up under the action of tectonics. Indeed, even the nearest of our galactic neighbours – Andromeda and Triangulum – are far enough away that the light from their constituent stars had been travelling across space for more than 2 Mly before being captured by my astrophotography setup.

One more thing I ought to mention in this introductory section is the fact that the concept of a ‘galaxy’ as we now understand it wasn’t established until the twentieth century. They had been observed before that; indeed, the first recorded observation of Andromeda (by Abd al-Raḥmān al-Ṣūfī) dates from 964 AD. For most of the millennium that followed, what we now know to be galaxies were classed as nebulæ. The famous ‘don’t-bother-looking-at-these-because-they’re-not-comets’ catalogue began in 1774 by Charles Messier, eventually included 39 diffuse objects which are, in fact, galaxies. Until the work of Henrietta Leavitt in 1912, which was built upon by others in the following decade and then encapsulated and explained in 1923 by Edwin Hubble, no-one could say definitively that they were distinct bodies far outside our own galaxy.

Let’s start with our nearest-neighbour galaxy, Andromeda, listed as M31 in Messier’s catalogue. It’s a barred spiral galaxy some 2.5 Mly away and a constituent of our local group of galaxies. There are approximately one trillion stars in Andromeda, compared to about 400 billion in the Milky Way. It’s close enough to the Milky Way that our mutual gravitational attraction is drawing the two galaxies together; there is an approximately 50% probability that they’ll merge [ii] in a few billion years to form a large elliptical galaxy. Indeed, current models suggest that Andromeda is itself formed from the merger of two galaxies – one being significantly smaller than the other.

Taken together, the three images of M31 illustrate the evolution in my astrophotography equipment and image processing. On the left immediately above is the first image I generated of Andromeda; it’s still one of my favourites as it shows the dust lanes nicely, a couple of dwarf companion galaxies and even an active star-forming region. On the right is an image generated by the pet robot I introduced in my previous post. At the top, on its own, is an image derived from the same data using a different processing method – the dust lanes still show up well, but the noisier outlying regions of the image are de-emphasised and the visibility of the foreground stars is greatly reduced. 

Although the third largest galaxy in our local group (after Andromeda and the Milky Way) the Triangulum galaxy contains only about 40 billion stars. Thus, despite its closeness – it’s 2.7 Mly away – it appears far smaller than Andromeda in the 1.4° x 1.4° frame of my setup. This is one of a great many targets I really ought to revisit as the image is quite noisy: as I recall, unexpected clouds appeared after only a couple of hours; c’est la vie.

While we’re on the subject of galactic-scale mergers, this pair of galaxies, M51a and M51b, are observed doing exactly that. The larger of the two, M51a (the Whirlpool), is a little smaller than the Milky Way; they are both approximately 24 Mly away, with M51b sitting behind M51a from our perspective. Current models suggest that M51b has already passed through M51a once before being pulled back through to its current position. There is evidence of the ongoing merger visible even in my amateur image: there is, for instance, an evident ‘bridge’ of material stretched out between the two, and the spiral arms are distorted. This process of merging may take another one or two billion years to complete.

On a more modest scale, the two pairs of galaxies shown above are also interacting, though not obviously merging. On the left is a pair of galaxies seen edge-on which are about 30 Mly away. The larger/brighter one is called the Whale, NGC 4631; notice its pup just beneath – a dwarf galaxy rather like those associated with our Milky Way. Above left is a smaller galaxy (the Hockey Stick/Crowbar, NGC 4656/57); even in my amateur image one can discern a distorted shape to one side – this is ascribed to a gravitational interaction with the larger Whale. The blue tinge to its distorted lower arm comes from the presence of a region of intense star formation – perhaps caused by the gravitational interaction. In the right hand image we have a pair of interacting galaxies 59-60 Mly away but only ~ 150 kly apart. (Unfortunately, the information available online is sometimes contradictory but I have tried to sift out the more reliable information.) As with the other pair, their gravitational interaction has distorted their shapes. It’ll be hard to make out in a blog post unfortunately, but above the brighter of the two (NGC 3718, image centre) is a group of very much more distant galaxies – Hickson Group 56. They are ~400 Mly away!

My very first galactic targets were this circumpolar [iii] pair: Bode’s galaxy (M81) and the Cigar galaxy (M82) which are both near The Plough. Bode’s, named after its discoverer who was (you guessed it) Herr Bode, is a spiral galaxy seen at an angle. The Cigar galaxy is pretty much edge-on; it has a distinctive red-coloured dust lane which obscures the galactic core. Both are approximately 12 Mly away. My very first attempt to capture this pair came before I was able to guide my telescope and the result was lamentable: I was barely able to discern the core of Bode’s galaxy, let alone any details of the spiral arms etc.

From pairs to triplets. On the left the Leo Triplet of spiral galaxies – which may be seen within the constellation of … Leo. Their orientation with respect to our perspective varies from edge-on to near full-face; all three are ~35 Mly away. The image on the right shows another triplet, this time appearing to be in the constellation Draco. The galaxies are considerably further away from us (112, 123, 140 Mly) and therefore appear much smaller; despite their separation from one another they are still regarded as being within an identifiable group.

At ~24 Mly away, the spiral galaxy M106 is almost ten times the distance to our nearest neighbour, Andromeda. However, it’s about the same size and luminosity as Andromeda and therefore shows up nicely in this back-garden image. Apart from its intrinsic beauty, I love the fact that so many other, more distant galaxies appear in the frame: it astonishes me still, after several years of astrophotography, that there is so much to see within every tiny patch of the night sky. This is photo-bombing on a cosmological scale.

I have only ever attempted one mosaic in the course of imaging galaxies and galactic groups and this is it: Markarian’s Chain (after Armenian astronomer Benjamin Markarian). The group comprises eight galaxies at distances of between 50 and 60 Mly. There are, however, another 18 galaxies appearing in this 1.9° x 1.4° frame: 26 in total!

Not to be left out, other than in terms of adding a lot more words to an already long post, I finish with images of individual galaxies that simply caught my imagination at a time when I could see them for a decent amount of time from my garden. Each one beautiful in its own right.

For another astrophotography blog post to emerge I need more clear nights. Sadly, the past two Autumns have been characterised by clouds – a consequence of climate change perhaps – and I must practice the virtue of patience 😉

Endnotes:
[i] ‘The hitch-hikers guide to the galaxy’ by Douglas Adams (Pan Books Ltd, London, 1979). The book was based on the original BBC Radio 4 series of the same name which ran from 8th March 1978 to 12th April, with subsequent series to come later. I remember listening to this late-night innovative radio play with rapt attention, along with my wife and a couple of friends in their bedsit in Leicester. (One of those friends went on to become a professional astronomer, spending years working on the IRAS infra-red telescope.)
[ii] I much prefer ‘merger’ over ‘collision’. Whilst the latter makes for good headlines, it really doesn’t convey the process: there may be some individual stars that collide, but the spacing between stars is such that direct collisions will be relatively rare. That’s not to say there won’t be dramatic consequences; gravitational interactions will disrupt both galaxies for many millennia, including generating compression fronts in gas/dust clouds that will lead to the formation of a new generation of stars.
[iii] By circumpolar I mean that they are close enough to the celestial pole that they can be observed all year. (The range that is ‘close enough’ depends on one’s latitude; for my garden at 51° N there are quite a few constellations – Ursa Major/Minor, Cassiopeia – and nebulæ and galaxies that fall inside the definition.)