Its SuperSonic! - G65.3+5.7 Supernova Remnant in Cygnus
Askar FRA500; iOptron HEM27;
ASI6200MM, - Baader Cmos optimized RGB & 6.5nm Narrowband Filters
2x2 Mosaic
H,O: (175,140 x 780s Bin 1, Gain 100) R,G,B: (82,82,75 x 180s, Bin 1, Gain 100)
Total integration time = 76.3 hrs (June 13,14,18,20,22to24 & July 1to8,18to20,23; 19 nights) Maple Bay, BC
If I were to pick an astrophotographic nemesis it would be this supernova remnant (SNR) within Cygnus. In data gathering, this was a huge struggle against weather, short nights, and a rotation issue. The remnant is HUGE – requiring a 2x2 full frame mosaic meaning it is like gathering data for four separate images. (to get a sense of size, that tiny globular cluster is actually M57 on the LHS) The object is also very faint requiring many long exposure narrowband images to get a decent signal. Finally, the SNR is within a very rich starfield, which obscures portions of the SNR. Processing was difficult – not only just because it was mosaic, but because the starfield varies in intensity and the background often contains faint nebulosity, getting a fix on the background gradients was difficult. The stars had to be kept small (and faint) in order to avoid obscuring the SNR. This took me at least 24 hours to process. Anyways, that’s just about my limit for spending time on a single image.
As for size, the image at full resolution is almost 100 Megapixels and occupies over 1.8 Gigabytes of file space. Consequently, a highly compressed jpeg is shown here.
One of the reasons I wanted to get this images (besides being a challenge) was to investigate what happens to material ejected from the star during its implosion/explosion. The result shown here is what happens when a very short duration explosion results in material travelling at supersonic speeds relative to medum around the star (whatever was hanging around the star). The speed of sound in a gas is related to its compressibility and governed by the pressure diffusivity equation. Essentially the more compressible something this, the slower sound – another word for pressure waves. Gases in space are very low pressure, resulting in high compressibility and a slow speed of sound.
When atoms and ions are shot out during a supernova it is done supersonically relative to the other atoms and ions surrounding the supernova. The high speed material collided with the stationary material sending both radially outward. This collides with more and more material, creating a dense wall of material sweeping up any intervening stuff as it goes. This is known as a shock front – I think because it is both a physical and emotional shock to any material that encouters it – there is no warning from the pressure as there would be in subsonic flow. At a certain radius, a pressure gauge would show an almost instantaneous jump in pressure as the front arrives, followed by and jump back down to an almost pure vacuum as the “shock front” passes.
These shock fronts can be seen as curved planes of material at the shock front, which is seen best from the side. As the shock front passes through various patches of space with different materials, the speed of the shock front will vary and the shock wave can interfere with itself. This is particularly true if the supersonic front encounters any condensed material along the way. This is interference is likely why we get the “bubbly” appearance of supernova remnants.
What we see in the supernova remnant are the shock fronts of material still moving outward from a long ago supernova. Within the shock front material is likely heated to a huge temperature by Joule Thomson effects and may be the energy source causing emissions, but I’ll have to do some more reading to confirm this. To further complicate things, it appears that this supernova erupted within a hydrogen cloud and we are seeing the red Ha emissions likely from both the yet undisturbed cloud and the SNR.
Eventually the shock front will be slowed – both by radial geometry and the considerable drag that any encountered material creates on the shock front. When the front eventually becomes slower than sound, the sharp front will disperse somewhat, which may be occurring within this SNR in portions.
