|(click on image for full resolution image)|
The Double Cluster is relatively young (12.8 million years) and appears to be slightly blueshifted. This is a result of its movement - it races towards earth with 38/39 km/sec!
The cluster can be seen with the naked eye in really dark areas and easily with a binocular. It was discovered 130 B.C. by the greek astronomer Hipparcus.
Both nebulae are actually one gigantic complex that is 300 light years wide! They are connected by a bridge of gas. Both are birthplaces of stars in their center (which is why their centers are less red: a lot of gas has already been consumed by new stars). The stars in their centers are just a few million years old - and they are younger the further they are away from the center.
Processing this image was made difficult by the bloated stars in the LRGB images:
I compensated for this already in the linear state by shrinking the stars using the MorphologicalTransformation process in Pixinsight (again, using one of he awesome tutorials on lightvortexastronomy.com):
First, I created a "contour star mask" from the stretched image:
This star mask should cover exactly the stars. Here is how the inverted mask looks::
Now, we apply the MorphologicalTransformation process:
And here is the result before and after:
It's a subtle difference (which is good as we don't want to completely change the image) - but makes a huge difference further downstream.