Ha enhanced LRGB image
Object description:NGC 6604 is an open star cluster around 5500 light years away, located in the constellation of Serpens. It forms the densest part of the wider Ser OB2 association, which contains about 100 OB stars. These stars excite the surrounding large HII emission nebula - Sharpless 54 (Sh2-54) - which belongs to an extended nebulosity that includes also the Eagle Nebula less than 2 degrees to the south of this image.
The combined effect of winds and radiation from the many OB stars has produced a rim of dense molecular material in which second-generation star formation is currently taking place. The most prominent is the brightest patch in the upper middle of the image - known as Gum 85 (Gum, 1955) and M1-88 (Minkowski, 1946).
In this crop, the nebula M1-88 is seen within a cometary like globule where a loose infrared cluster of massive young stars has recently formed.
Reference:
Reipurth, B. (ed.), The Young Cluster NGC 6604 and the Serpens OB2 Association, Handbook of Star Forming Regions Vol. II, Astronomical Society of the Pacific (2008)
https://pdfs.semanticscholar.org/f821/acd3aad6d2b966c264ac64a09a075d5da8fe.pdf
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