Sharpless 2-157 (the Lobster Claw Nebula) in the constellation Cassiopeia consists of a bright core surrounded by an irregular cloud of ionized gas, with two arcs extending to the northwest in a claw-like shape.
The claw's "pincers" form a ring around the small open cluster Markarian 50 (left of center just above the bright blue arm in this image). This cluster is relatively young at an estimated 7.5 million years, and contains the Wolf-Rayet star WR 157. Wolf-Rayet stars represent a late stage in the life of hot, bright O-type stars, and emit copious amounts of radiation and stellar wind. The gas shed by these stars collides with the surrounding interstellar material, forming a ring-like shock wave. Compression of the interstellar gas can then trigger subsequent star formation, and infrared studies of the region around the "claw" have indeed found numerous protostars in the process of coalescing. (
https://ui.adsabs.harvard.edu/abs/2009MNRAS.395.2045V/abstract)
Note in the upper left is another small open cluster, NGC 7510. I couldn't find anything indicating whether this cluster is directly related to Sh2-157, although they both seem to be associated with an extended star forming region known as Cas OB2.
This image is the product of three nights of imaging, and incorporates 60x60 seconds red, 100x30 seconds each green and blue, 60x300 seconds Ha, 75x300 seconds OIII, and 75x300 seconds SII (total is a bit over 20 hours). Taken with a 115mm refractor, and the first image using my new Mach 2 mount.
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