Sh2-181 and 183

Sh2-181, the hook shaped region at the top of the formation surrounded by a blue halo, is a bit of a mystery. Distance estimates range from 6,500 to 8,800 light years. But the real conundrum involves the origin of the blue halo, which comprises ionized oxygen gas.

As my friend Göran Nilsson has speculated, this may be the result of strong stellar winds from the hot star WR1 (located just out of the frame). But working against this idea is that the distance estimates I’ve found for WR1 place it more than 10,500 light years away, which means it would be around 2,000 light years from Sh2-181 (depending on the accuracy of both distance estimates).

In the image, it looks as though Sh2-181 and the much larger Sh2-183 below it are part of a single gas complex. But the distance estimated for Sh2-183 comes in at around 22,830 light years. This would imply that these are completely separate entities that reside at least 14,000 light years away from each other.