So the coordinates from the random number generator have hit another Messier object. It's actually been over a year since the last time that the generator selected one. This object is the spiral galaxy Messier 74 (M74), and it's one of the prettier objects in the Messier Catalogue. It's a spiral galaxy with two very distinct spiral arms that is seen from Earth nearly face-on, or in other words, we are looking at this galaxy from a direction nearly perpendicular to the galaxy's disk. Given this and given that the galaxy is only 32 million light years (9.8 Mpc) from Earth [1, 2, 3], we have excellent views of the spiral arms in this galaxy. Additionally, the galaxy has a diameter equivalent to about one-third the diameter of the Moon as seen from Earth [4], so its possible to see a lot of extended structure within the galaxy. The one downside is that it has a relatively low surface brightness (or brightness per unit area), but I'll get to that later.
For people who don't know the story or haven't heard my previous podcasts about other Messier objects, the Messier Catalogue was compiled by the eighteenth century astronomer Charles Messier, who wanted to be known for the comets that he discovered but who is actually remembered for compiling the first list of star clusters, nebulae, and galaxies. He basically created this catalogue of fuzzy objects that weren't comets because he just wanted to keep track of these "false discoveries" so that he could stay focused on comet identification.
The galaxy Messier 74, like a few of the objects in the Messier Catalogue, Messier 74 was not discovered by Charles Messier himself but by Pierre Mechain, an eighteenth century French astronomer who also wanted to be known for the comets that he discovered but who is actually remembered as Messier's sidekick. Mechain discovered the galaxy in September 1780 but noted that it was really hard to see [5]. Messier confirmed the sighting and that it was really hard to see the next month [5].
By the way, while Messier 74 or M74 are the most generally-used names for this galaxy, most professional astronomers (including me) commonly refer to this galaxy by its New General Catalogue (NGC) designation, NGC 628. Some amateur astronomers call this the Phantom Galaxy because it's hard to see, but I personally think that name sounds like something corny from the Star Wars prequels, so I'm never going to use that name.
I honestly would have difficulty trying to pin down what makes M74 scientifically important. It doesn't have any specific trait or property that makes it stand out from other spiral galaxies, and while it is close to Earth, quite a few other spiral galaxies are closer. Instead, I would suppose that what makes this spiral galaxy really interesting scientifically is that it is just a very nice example of a spiral galaxy, and that in and of itself makes it quite useful for a couple of specific types of analyses.
First, because Messier 74 is such a nice face-on spiral galaxy, it has been a popular object to observe for studying the dynamics of the spiral arms. While people once thought that galaxy’s spiral arms were permanent structures made of stars and interstellar gas, we now know that spiral arms are actually formed by density waves propagating through the disks of spiral galaxies. Stars entering the spiral arms will just sort of slow down, which will make the density of stars in the spiral arms a bit higher than other parts of the galaxy’s disk, but they will eventually pass through. Interstellar gas clouds, however, will get compressed, and this will lead to the gas clouds collapsing to form new stars. In fact, multiple studies of Messier 74 specifically have shown that star formation is quite enhanced within the galaxy’s spiral arms [6, 7, 8, 9]. One recent analysis even showed that, in some parts of Messier 74, gas could be seen going into one side of the spiral arms, and new stars could be seen coming out the other side [10].
Messier 74 has also been a popular target for astronomers who want to understand the formation of elements larger than hydrogen and helium. These elements are mostly formed either in the interiors of stars or when the stars die and expel their outer gas layers to form planetary nebulae (as would be the case for stars like the Sun) or as supernovae (as would be the case for stars much larger than the Sun). Since the centers of galaxies are generally older than the outer parts, astronomers should be able to see variations in the ratios of things like oxygen to hydrogen or iron to oxygen as a function of the galaxy’s radius. Messier 74 was not the first galaxy where radial variations in these ratios were measured, but it was one of the first [11], and these ratio variations have been studied extensively for decades [11, 12, 13, 14, 15, 16]. What is learned from Messier 74 specifically regarding these heavier elements can then also be applied to other galaxies more generally.
Many other professional astronomers have performed studies with Messier 74 for multiple other reasons as well as the two I just mentioned. For example, quite a few supernovae have been seen in Messier 74 [17, 18], and since the galaxy is relatively close to Earth, it’s a good place to study those supernovae in detail. I myself have used Messier 74 in a couple of my studies into interstellar dust.
To begin with, I have performed a few studies looking at a class of interstellar molecules named polycyclic aromatic hydrocarbons (PAHs), which contain multiple rings of carbon atoms, and I have demonstrated that, in general, emission from these molecules have been suppressed in the locations where stars are forming [19], most likely indicating that the molecules were destroyed by the harsh ultraviolet light in those regions. In areas around these star forming regions in many galaxies, including Messier 74, the emission from PAHs may be enhanced, indicating that the molecules get excited by the relatively weaker ultraviolet and visible light escaping the places where stars are forming [20]. This means that the emission from PAHs could be used to measure the rate at which stars form but only on large scales.
Additionally, I have demonstrated that Messier 74 is one of several galaxies where it’s possible to see interstellar dust heated by two different populations of stars. Some of the interstellar dust is heated by the youngest stars in the galaxy, and this dust is seen primarily at shorter infrared wavelengths, while some of the other dust is heated by older stars, and that dust is seen at longer wavelengths of infrared light [21].
However, the most spectacular science results to come out about Messier 74 recently have been the James Webb Space Telescope images of the interstellar dust in the center of the galaxy [22, 23, 24, 25]. These images mapped structures as small as 80 light years, which is much more detailed than any infrared images of the galaxy that I had worked with in the past. The new data revealed the presence of a complex web of filamentary structures running between bubble-like regions of hot gas both within the spiral arms and in between the arms [22, 23, 24, 25]. Such filamentary structures had been seen in our galaxy using older infrared telescopes but had never been mapped in such detail in another galaxy. These filaments of dust, which also contain cold interstellar gas, are basically the location where stars are forming [22]. Meanwhile, the bubble-like regions are places where stars have already formed. The bubbles are produced by a combination of ionization by the hottest stars in these regions as well as supernovae [23, 24, 25]. These pioneering images with Messier 74 are just a prelude to what the James Webb Space Telescope will be able to see in other galaxies in the future.
If you would like to see Messier 74 with your own telescope, it’s a bit tough, but it is possible. The galaxy lies within the constellation Pisces, which has a sort of V shape with one part of the V going north and the other going west. To find Messier 74, I recommend identifying Eta Piscium, which is the third star from the vertex on the northern branch of Pisces; the galaxy will be located 1.5 degrees east northeast of this star. Keep in mind that the galaxy has a low surface brightness (or brightness per unit area), so to actually see this object, I recommend observing from a dark site on a moonless night and also selecting low magnification eyepieces so that the light does not get spread out too much. Using a telescope with an aperture as small as 7.5 cm (3 inches), it is possible to see the center of the galaxy, but it will look like a faint hazy disk [26]. In an 8 inch (20 cm) telescope, it will be possible to see a distinct difference between the center of the galaxy and the disk [26], while in a 12 inch (30 cm) telescope, it is actually possible to begin to see the spiral arms [26]. This is one of the most challenging objects to find in the Messier Catalogue, so if you decide to try to see it yourself, good luck.