The Rubber Chicken of Creation – Barnard 175 in LRGB
Askar 151phq; AP Mach2 GTO ASI6200MM, - Chroma LRGB L: (92 x 150s 61 Bin 1, Gain 100) R,G,B: (44,47,40 x 180s, Bin 1, Gain 100) Total integration time = 10.4 hrs (July 31 & Aug 2, 2024) Maple Bay, BC
Followers of my recent images images may be aware, that I have set about trying to include thermodynamic and fluid mechanical concepts into the story of star creation making it consistent with how real susbtances behave. Sort of like the old radio program “The Rest of the Story”. As it turns out, adding these concepts is very helpful is filling in the gaps in the conventional story and that it takes more than gravity to make a star.
This image is of a shrinking (or condensing, or collapsing) molecular cloud globule, called Barnard 175, that is also being eroded by a current of less dense interstellar medium. The visuals and SIMBAD queries show that all of the ingredients are here for the thermodynamically consistent star formation:
External sources of light and material warming and pressurizing the extremities of the cloud
Dark areas of the cloud where visible light (and UV) cannot penetrate or escape
Areas of IR, far IR, and radio emissions, more free to escape the inner parts of the cloud, where hydrogen is being cooled.
Young stellar objects - both visible in the image, and revealed through IR imaging
Aside from star formation and cloud “collapse”, erosion of the molecular cloud is taking place, indicating that the molecular cloud is moving somewhat relative to the surrounding interstellar medium, likely as a result of weak stellar winds, as evidenced by the slight red Ha alpha emission streak running diagonally from the bottom of the image. Other images that include narrowband data in this image, show extensive, but dim Ha emissions caused by UV. It appears that these emissions are occurring in the background to the cloud.
Our chicken was likely encased in larger, but less dense molecular cloud at some point, leaving the higher density, colder chicken behind. Remnants of this larger cloud can be seen in the dusty nature of the image, particularly on the left hand side. On encountering the chicken, however, the winds prefer to go around it, because there is too much inertia to accelerate it. Colder parts of the chicken stand out defiantly against wind while other parts seem to bend under the wind’s onslaught, and only slowly succumb to erosion, leaving trailing whisps of reflecting dust.
The chicken itself is bathed in whisps of reflecting dust likely becoming disperse in the wind. The body of chicken is being eroded by both head on collisions and shear forces caused by the velocity gradient between the cloud and the interstellar medium. A keen eye will see that this is not just a dispersive action of elastic collisions (ideal gas) on the hydrogen that makes up the chickens body, but rather more like sand grains being blown off the top of dunes. The chickens body itself is almost parallel to the ISM flow, so where does this erosional force come? A closer examination reveals that a lot of the erosion is actually coming off the sides of the chicken and molecular cloud outliers.
It is in fact shear forces as transmitted via the viscosity of both the ISM and the molecular cloud as they move past each other. On a molecular level, the viscosity (resistance to shear) is caused by our old friend, Van der Waal forces. Although hydrogen molecules do not have a dipole moment caused by angular bonds or dissimilar atom, when two molecules either approach each other (collision) or try to move past each other (shear), their fluctuating electron positions with induce a magnetic dipole on each other, creating a stickiness order of magnitude greater than gravitational force. If the molecules are moving past each other (shearing) in a gas, the fast moving molecule will start to drag the slower moving one to move with it. The slower moving molecule in turn presents a drag on the fast one, slow it down. On a molecular level, this resistance to shear is called kinematic viscosity. In a gas, the kinetic energy of the molecules is too great for them to stick together for long and the molecules will separate again.
As the ISM flows past the molecular cloud, it set up a shear force the pulls material off of the molecular cloud – much like the air moving over an airplane wing tugs it up. This is how a moving ISM or solar wind erodes around a pillar,finger or elephant trunk in a star forming area and often exposes the stars being created within it.
Before anyone suggest that the gas in molecular clouds are too rarefied for Van der Waal forces to even be considered, and this false assumption often mistakenly leads to the assumption that the hydrogen behaves ideally. However, even in a rarefied environment, it is in the collisions of molecules where all the interesting things and important things happen. Kinematic viscosity being a per molecule (like temperature) scales linearly with density to create bulk viscosity (just as temperature linearly scales with density to create energy). The kinematic viscosity of a gas is a function of temperature only, and not pressure or density. Here is a fun and interesting video illustrating this. The rarefied nature of the molecular cloud, or even the ISM/winds does not make them behave like a simplified ideal model where collisions can be represented like marbles hitting each other.
In any even we are only able to see this stage of star genesis by the erosion of the outer shell of cloud and dust by the interstellar material, moving from right to left in the image. The head of the chicken is predominantly blue (with a hint of red Ha), but a pixel peep reveals a bright young stellar object (or protostar), with its hot blue light reflecting off the dust in the vicinity. I would hazard to suggest that this star is in the latter part of its mass accumulation stage.
One explanation for the spiral patterns of the reflections may be that they are dense tendrils of material being drawn into the protostar by gravity, like water going down a drain in a bathtub. During its accumulation by gravity stage or star development, the material must shed a lot of its angular momentum to avoid simply orbiting the protostar and in effect “missing the star altogether”.
Angular velocity will try to accelerate as it approaches the protostar. The material, in effect, tries to pull away from material slightly further away. However, due to molecular stickiness (Van der Waal and viscosity again!) the molecules tug on each other, slowing down the molecule in front, and accelerating the one behind. This tugging and holding back continue along the length of the spiral. This tugging chain, caused by the molecular stickiness (viscosity again!), actually slows the material as it gets closer to the star, allowing it to eventually fall into the protostar and become a part of it. At this stage, it is likely that the protostar hydrogen would exist as a super-critical phase that remains a condensed (incompressible) material due to its own hydrostatic head - avoiding a return to the gas phase and self destruction as its temperature rises.
The ability for a gravity to accumulate material to a protostar is highly dependent on the ability to shed the material’s angular momentum as it falls. If it does not, it will simply start to orbit the protostar. (Here is another fun and informative video on why we cannot practically just dispose of spent nuclear fission fuel into the sun.)
At the same time as moving angular moment outwards away from the protostar, viscosity tends to conform the angular momentum of the material falling into the protostar – slowing down the faster molecules and speeding up the slower ones. This results in a concentration of material within the spiral, and all spiraling at roughly the same speed. It is this concentration of material that yields the reflections we see as the spirals themselves.
An alternative explanation of the “swirls” are that these are errant Herbig Haro jets, which Remaining angular momentum will be shed via Herbig Haro jets emanating from the rotational poles of a protostar, but this stage likely relies on the protostar undergoing a transition to a liquid metallic state to become the electromagnetic dynamo that can convert the angular momentum into linear jets. The blue colour of the light may indicate that the temperature of the protostar is high, indicating that the star is indeed metallic (in the true sense), but then again it might be “bluified” (preferential adsorption of red) by the dust it is reflecting of
