IC 4628 (Gum 56, Ced 137b, Prawn Nebula ) in Scorpius

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IC 4628 (Gum 56, Ced 137b, Prawn Nebula) is an emission nebula located south of Antares about 6 000 light-years away and it is about 250 light-years across. It is observed in the southern part of the constellation, just north of the bright open cluster NGC 6231, which is also located in the same galactic environment. It is an HII region that directly receives the radiation of the massive stars which forms the core of NGC 6231 - Scorpius OB1 association. The main ionizing star is, according to a 1984 study, the blue giant HD 152723. Other sources suggest that the ionizing source is the star HD 322417, also a class O5 or O6, although this may be at a distance greater than the region of Scorpius OB1.

Over the last few million years this region of sky has formed many stars, both individually and in clusters. Also visible are many dark structures or cavities, where interstellar matter has been blown away by the powerful winds generated by the nearby hot stars.

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