Narrowband Rorschach Test in LDN900 area in Cygnus
Askar 151phq; AP Mach2 GTO
ASI6200MM, - Chroma RGB & 5nm Narrowband Filters
H,O,S: (34,30,24 x 720s 61Bin 1, Gain 100)
R,G,B: (17,23,23 x 120s, Bin 1, Gain 100)
Total integration time = 19.7 hrs (July 5 to 8, 2024)
There is a lot going on in this image with every nebula type we would see through our telescope – emissions, reflections, and dark nebula. I chose this target because I wanted to see some variations in nebula structure with a focus on transparency as backlit by both emitting nebulae and stars. It is via backlighting and reflections that we can see dark nebula at all, as there is little visible light coming from them directly at all and they tend to block light from passing through them from behind. Artists call this negative space.
In this image, there is negative space all over the place, with the largest structures including a large “mustang/colt” shaped dark object facing left, next to an large ugly dark “X” dominating the LHS. On the RHS, are many smaller dark nebula appearing like ink spills over the image. Reflections from the dust can also be seen as deep blue patches of light bouncing off the dust from somewhat nearby stars hitting the dust at just the right angle and distance.
The reason why these nebular regions appear dark or even black is that they contain condensed material (solids or liquids) often called dust that can reflect or adsorb light that attempts to go through it. The ability to block light gives us an indication of the density, thickness, and dust concentration of the molecular cloud. This light blocking ability can be seen in variations in the brightness of the emission nebula, star size and magnitude of the stars behind it. Infrared light more readily pass through the dusty molecular cloud, but the dust can get so thick that only radio waves can pass. Reflections from the dust can also be seen as deep blue patches of light bouncing off the cloud from somewhat nearby stars hitting the dust at just the right angle and distance instead of passing through into the cloud.
Dark nebulae are likely initially formed by eddies in the molecular cloud being pushed around by stellar winds and tidal forces occasionally creating knots of higher density. If there is sufficient dust, very little warming light can get into the already cold cloud knot and it will shed net heat further increasing its density and reducing its temperature further still. Parts of the dark nebula in this image, are so think/dense that it seems no visible light from the other side can get through to reach the camera.
Dark nebulae are important as this where new stars are conceived. I surmise that If the internal parts of the cloud get cold enough, any helium and even hydrogen will condense as “dew” or “frost” once the temperature/pressure conditions are reached – below, say 10 or 20K. The heat of condensation can slowly be shed via radio waves (approx. 200 microns) outwards past the dust. It seems likely that coalescence of this now condensed material through a random walk process can eventually reach a mass where gravity can take over the hydrogen accumulation process that can eventually result in a new star.
I am not sure if any new stars are currently being formed in the dark nebular clouds in this image, or even if this is really the nature of the process because the dust also prevents us from have a propper look inside. This target doesn’t make for the prettiest of images, but it is pretty interesting.
