At first glance, Messier 63 (M63 for short or aka “the Sunflower Galaxy”) appears to be a break from the traditional spiral structure of galaxies and represent a new type of galaxy termed a “flocculent” class. It was thought that the stars formed clumpy clouds gathered together as clumps, like strands of wool form clumps of wool – even on the sheep.
In chemical engineering, we often use agents that make particles suspended in a fluid clump together to form larger particles ,so that gravity can overcome the suspension and separate the particles from the fluid. I like to thing that the word flocculate (or its sorter “floc”) comes from the word “flock”, as in a flock of sheep, but I have no idea if this is true. In the case of M63, the clumpy appearance of the galaxy resembles, as a whole, the face of sunflower where the clumps are replaced by the flowers’ seeds.
In reality it is the outline of dust lanes in the molecular clouds that are primarily responsible for the galaxy’s clumpy appearance as a floc. However, I can still make out the vague pattern of a spiral in the galaxy in our images, so perhaps M63 is not so different after all. In addition to the spiral dust lanes that only marginally dominate the view of the galaxy, there are “en echelon” dust lanes – ie. dust lane arcs that intersect the main spirals at an angle to the main spiral trend.
In the end, the flocculent appears isn’t a entirely new class of galaxy, but rather a spiral galaxy in sheep’s clothing. As we shall see, even in the most ordered of galactic spirals, there are additional molecular clouds and dust lanes other than in the main spiral arms. The presence of these additional dust lane arcs present another mechanism for the circulation of hydrogen and dust throughout the galaxy. Hydrogen can move between arms in two ways – it doesn’t only have to just move between spiral arms in monatomic form between arms as I described in this past posting. Additionally hydrogen can move between arms either as strands of cloud, or even within arc bridges that completely connect the arms. What M63 flocculent reveals in visible light is just an exaggeration of what the JWST telescope and other IR images show in at least most other spiral galaxies – that either as clumps, strands, or even within arc bridges, molecular clouds of diatomic hydrogen molecules can travel between the main spiral arms.
The Sunflower Galaxy, M63, in LHaRGB (Canes Venatici) , May 2023
Planewave CDK12.5″ telecope; A-P 1100GTO AE mount; ASI6200MM Camera, Antlia Pro BB & 3.5 nm Ha Filters
Lum: (66 x 200s exposures, Bin 2×2, Gain 100); RGB: (3 x 28 x 240s exposures, Bin 2×2 Gain 100);
Ha (22 x 400s exposures, Bin 2×2, Gain200); Total Integration Time = 11.7 hours
While I prefer to base my postings on new images, this galaxy escaped by target list for 2025, and I find myself having to post this two year old version when both my skills and the software utilities in processing images were undergoing a step change in improvement. To add to this, my notes and close examination indicate that my Corrected Dall – Kirkham (CDK) telescope was slightly out of collimation. In any event, the flocullated appearance of this galaxy was puzzling to me at the time, and only completely clarified when I saw JWST near-IR images of other galaxies. That left me no choice but to dig up this, over two year old now, version.
Other odd-ball characteristics of M63 include the fact that, there is no “donut hole” or bar, at least visible, at the galactic centre. The galactic disc appears to be supplying whatever is at the centre with material that ends up spiral into it. Within this “death spiral” or more formally “accretion disk”, the strong viscous and electromagnetic forces heat up and excite the material. This material yields spectral adsorption and emission light that yield its atomic composition. For this reason, we classify M63 as a LINER (galaxy, with a “Low – Ionization Nuclear Emission Region), characteristic of a mild to moderately active core.
Accretion discs tend not to be planar like most of the galactic spiral – the top and bottom of the spiral curve in towards the point source causing the galactic disk to thin and bend to fit the spherical coordinate system that prevails close to a black hole. When a galaxy is viewed obliquely, as M63 is, this can hide the central attractor from view. As a result, we don’t really know what is at the centre of M63 – could be a black hole, or a neutron star, or a dense globular cluster of stars – we simply can’t see it. Rest assured, however, this is all fodder for a future posting.
The curving/thinning of the disc can reveal dark dust lanes on one side of the disc near the core and this can reveal what side of the galaxy we are looking at. In this case the top side in the image is closer to us and we are looking at the galaxy from underneath.
Most galactic spirals extend invisibly well beyond their visible radius (again fodder for a future posting) and M63 is no exception. While the visible portion has a radius of 90 to 130 thousand light years, but the invisible portion – detectible only via the 21 cm radio emissions of atomic hydrogen, has a radius several times that.
For high resolution, downloadable versions of this image please visit Victoria RASC Zenfolio site or Astrobin
Askar 151phq Refractor; AP Mach2 Mount; QHY600M, – Chroma Broadband and 6.5 nm Ha Filters
L: (77 x 100s, Bin 1, Gain 100); H: (49 x 600s Bin 1, Gain 100); R,G,B: (47,49,51 x 120s, Bin 1, Gain 100)
Total integration time = 15.2 hrs (Jan 24-28, 2025) Vancouver Island, BC, Canada
For high resolution, downloadable versions of this image please visit Victoria RASC Zenfolio site or Astrobin
Hydrogen and Dust
Hydrogen is by far the most abundant element in the galaxy, make up 75% of the total mass and over 90% of the individual atoms. In a spiral galaxy such as M63, most of the hydrogen exists either as atoms or as diatomic molecules withing the arms of the galaxy – the proportions of which depend on the pressure/density within the arms via the association/disassociation simple reaction: “2H ↔ H2”. The higher pressure that exists in the spiral arms drive the association of hydrogen into molecules and this affects the gas properties. Molecular hydrogen can have weakly binding van der Waal forces on one another, in addition to exhibiting higher friction to fluid flow or viscous drag. The combination of self-gravity, together with viscous forces give the arms integrity, and hydrogen with the arms lose their independent body nature.
While the arms move around the galactic centre the hydrogen is somewhat locked into moving along the spiral arms and the individual orbits are essentially a superposition of the arms orbit around the galactic centre and the hydrogen s movement around the radius of curvature of arm. Within most if not all of the spiral the radius of curvature of the arms is greater than the orbital distance from the galactic centre (and this fact actually defines a spiral). This allows molecules to move along the spiral, closer to the galactic centre while viscous drag sheds angular momentum to heat.
As the hydrogen travels down the spiral, it can come to the turbulent interface with the extremely rarefied, but fast moving monatomic hydrogen flowing in the opposite direction in the gaps between the spiral arm. This flow is said to be countercurrent, or outward from the galactic centre. Here hydrogen atoms, and even molecules dissociating into atoms can joint the outward spiraling gap interstellar medium (ISM), only to be collected again by the next outward flowing arm. This process can result in a pseudo-steady state system where the flux of hydrogen molecules inwards within the arms matches the outward flow of hydrogen in the gaps as described in more detail in this posting.
But travel as an individual atoms is not the only way hydrogen can circulate between individual spiral arms. Turbulence and erosion can also cause large portions of the spiral arms to break off as clouds and begin to move as a molecular cloud unit into the gaps and then outward and across the gaps to the next spiral arm.
As we shall “see” shortly, these cloud units can be completely broken off, or broken off as tendrils still clinging at one end to the spiral arms, or even form bridges connecting the arms allowing hydrogen molecules to flow along the bridge between them.
I say we shall “see” shortly, because without stars or dust to trace the movement of hydrogen, this whole process happens invisibly to our cameras. (This also explains the lack of addition images so far in this post). In any event, within its “visible” radius, we can make out some of this process by the density patterns made by particularly young stars that do not live long enough to stray far from the molecular arms and clouds that created them.
A better tracer for molecular hydrogen’s movement is dust – heavier atoms, molecules, and particles than hydrogen that reflects or blocks starlight to us depending upon whether it is in front of or behind the stars. Dust likes the gravitational pull of molecular spirals and clouds. Through compositional grading, dust seeks out the core of the molecular clouds and spiral arms into order to establish hydrostatic equilibrium within them. In other words, dust likes to be in molecular clouds and spiral arms where it can do its visibility trick. It does not like to be in the ISM (with a few notable exceptions) so it become a great tracer for both the spiral arms and any molecular clouds between them.
The Molecular Cloud Network in M63
Behind a haze of stars that don’t seem to correlate well with any spiral arms, the patchy, or flocculated look is given to the remaining light given off by the galaxy. These patchy blocks are separated by dust lanes that form a dust lane network of both spiral pattern lanes and curved en echelon lanes between the spirals.
Since dust lanes exist within molecular clouds and spiral arms, this pattern should suggest to us that there is a high degree of molecular cloud tendrills, and even molecular cloud bridges between the spiral arms.
This is why M63 seems to have a flocculated character.
Dust is an essential ingredient or catalyst in creating new stars, that ultimately results in the creation of more dust. When cluster of stars are forming, atomic hydrogen is given enough excitement to emit Halpha red light, that our cameras can capture. In our image we can see many areas of bright Halpha red within the dust lanes indicating that star formation is indeed occurring at a healthy clip. In turn, this is indicative of substantial turbulence within the galaxy, with turbulence being a catalyst for both star creation and erosion of molecular clouds from the arms.
Dust does its work in the galaxy by cooling it off through near-IR emissions. By capturing M63 in infrared by the Spitzer space telescope, the dust emissions form an excellent tracer for where it and molecular hydrogen coexist.
Less obscured by starlight, we can see more clearly that the dust lanes are dominated by two spiral arms. At the same time, there are definite strong molecular cloud bridges between the arms that allow transport of hydrogen and dust between them.
Note that the bridges between the spiral arms also form arcs (fractal spirals?). These arcs have their convex side pointing in the same direction as the main arms, but see have smaller radii of curvature than their distance from the galactic centre. This would suggest that flow in the bridges of hydrogen and dust is countercurrent to that in the main spiral arms, i.e. outwards rather than inwards.
Now that we finally have some pictures, we can rest assured that M63 is indeed a spiral galaxy. It may indeed be appropriate to call it a flocculated galaxy, but now we know that just means a lot of molecular cloud bridges and erosion off the spiral arms.
JWST and the Molecular Cloud Structure of Galaxies
In early 2024, Nasa released over a dozen near infrared JWST images of spiral galaxies that gave us great insight into the structure of the molecular clouds inside galaxies. By capturing infrared light, the James Web Space Telescope can directly record light emitted by the dust itself as it cools the molecular clouds that contain it. Various galaxies were includes, as illustrated in this collage
In the image at left NGC 628, a visible light Hubble image of this barred spiral galaxy is compared with an infrared one by JWST. Not only are the dust lanes plainly visible in the IR rendering, but non ifrared light and the light from broadband emitters (i.e. stars) is greatly attenuated.
Dust when present, makes an excellent tracer for molecular clouds – ie. molecular diatomic hydrogen. To some degree, dust is held in suspension within the molecular clouds, and compositional grading attracts dust towards the centre of molecular clouds. There may be some dust within the much more rarefied monatomic ISM (gaps) between the molecular clouds, but if there is, there is little heat generated to create these IR emissions.
Dust, as well as molecular hydrogen, is required to create stars and so that newly born, short lifespan, hot, massive and blue stars also trace the outline of the molecular clouds, but only to a much more imprecise degree.
The thickness and density of the main spiral arms continue to make them the dominant dust lanes we see in galactic images, but the complex nature and flow patterns of the molecular clouds is often more obscured.
The first conclusion you are likely to draw from these images is that, to some degree all spiral galaxies exhibit some of the same “flocculated” characteristics as the Sunflower Galaxy, M63. Whether they appear as such or not, is partly dependent on the angle that we view the galaxy, how well the dust lanes are lighted, and how well their structure is obscured by other light sources and reflections.
From a material balance standpoint, we concluded that net of star production, the flow of hydrogen within the main spiral arms had to be toward the centre of the galaxy. To avoid accumulation at the centre, this means that there had to be a mechanism for hydrogen to move back out. I suggested that there was two mechanisms – either through the ISM or via the bulk transport of the molecular hydrogen outward between the spiral arms as they are eroded by ISM (or stars!) from the main arms.
The ISM is pushed outward by the rotation of the galactic arms. The inertia of the molecular arms act like the spiral impellers of centrifugal pump, forcing ISM outward. This direction is dominant in most parts of the galaxy, due to the nature of spiral geometry, where the radius of curvature of the spiral arms increases with distance from the galactic centre. But dust is not carried (much) through the ISM, so it must have another route to move outward through the galaxy. The importance of bulk transport of molecular cloud is of great importance to understanding galaxy dynamics, so it would be critical to know which way dust is flowing via the bridges that connect the spiral arms.
We have two aids to help us with understanding the direction of dust transport/molecular cloud in the gaps between spiral arms. The first help, is provided by understanding that the molecular clouds are eroded and carried by the ISM. Thus the molecular clouds should conform to their direction of movement and, when connecting the spiral arms, should almost follow the streamlines set by the rarefied, but fast moving ISM. We know this flow is generally from the convex side of an inner arm, leaving almost perpendicular to the arm and arriving tangentially to the convex side of the next spiral out. My review of the montage is that this is true.
A second aid to our analysis is via the radius of curvature and whether the molecular cloud “bridges” are convex or concave inward – just as we can use this to analyze the direction of flow within the spiral arms themselves. Within the spiral arms, viscous forces can reduce angular momentum and knowing that the inner spiral arm has lower angular momentum than an outer one can be used to work this out if a deep analysis of a galaxy where to be conducted. Such an analysis is beyond the scope of this posting, but would make for a great research project.
Rest assured that with only this bulk – between the arms mechanism – that it is much easier for dust to migrate inwards along the spiral arms than it is to migrate outwards via this arm bridging and jumping mechanisms. For this reason we believe that galactic star production tends to evolve outward from the centre and gradually moves outward. As dust reaches the outer radius defining the visible portion of the hydrogen spiral arms, moving further outward becomes more and more difficult. At the visible extremeties, the arms tend to grow farther apart making the bridge farther to establish and the jump longer and longer.
In most galaxies, the total radius of spiral hydrogen is much greater than just the visible part and M63 is no exception. Dust progress, and consequently star formation progress outward is a slow process. And yet progress is eventually made because there is one additional mechanism by which dust gets distributed around the galaxy.
Did we forget about the stars?
Before we get to the stars, we have to describe gravitational field that all of this material – hydrogen (and helium) and dust generates. In our postings on galactic structure, we showed that the spiral arms will create a gravitational field that is periodic in both radial and angular directions. Of course even molecular clouds in the gaps will add to the complexity of the gravitational field making it potentially periodic at higher frequencies. Viscous forces are what keep the molecular cloud from becoming a disperse mess.
Stars, with their comparably large masses, radii and inertial forces are far less subject to the conforming forces of viscous drag on fluid molecules in motion. Free of substantial forces, stars, while imparted with their initial inertial by the molecular cloud that made them, are free to go where the whims of gravity and angular momentum want to take them. Rather than pulling inward along the spiral, new stars will exit the spiral arms. Most will move inward and outward again due to the periodicity of gravity as they take their own paths around the galactic centre. In general, without viscous drag, they will hold on to their angular momentum and orbit faster than the spiral arms.
Hot, large, blue stars can still be seen aggregating around their spiral arm birthplaces, but this is because they generally die before they get too far away. Older stars, closer to the galactic centre seem to pay more attention to potentially orbiting the arms themselves, and to chance encounters with other stellar objects. The overall effect of this more independent movement of stars is dispersion. In comic books, dispersion is the arch enemy of viscosity. Viscosity brings uniformity of movement while dispersion sends stars all over the place – both within and outside of the galactic plane. What happens when the star encounters the spherical field of the central black hole, is even more dispersive, but that again is for another posting.
The dispersion of stars is important to dust transport, becuase within the stars is exactly where dust is created. Each star is a dust factory, and the dispersion of stars throughout the galaxy ultimately leads to the dispersion of dust throughout the galaxy. We just have to wait until the stars run out of thier fuel, and die in explosions that tend to scatter their dust.
In particular stars that are created close to the edge of the visible galaxy might send their dust farther outwards, allowing the visible galaxy to ultimate grow. We can’t say how far out the visible portion of M63 will eventually get before two many disperse stars end up messing up the spiral structure – at least within the visible radius.
I hope to get more into the evolution of galaxies at some point, but there are still a lot of t’s to cross and i’s to dot in future posts on this subject. In addition, there are a lot more galaxies to analyze too, while maintaining consistency with what has been described before. This is a long post already, so I hope you stay tuned and please send me any feedback via the home page
