Usually a massive, hot Wolf-Rayet star blasts away surrounding molecular gases and other interstellar debris more or less equally in all directions, forming a roughly spherical bubble. This hasn’t happened here; WR-18, also known by the catchy designation HD89358, has selectively sculpted a distinctive banana-shaped arc in one direction. Early studies of this nebula attributed the cause to bow shock, as a fast-moving WR-18 plows through interstellar material. However, a more recent
2017 study presents evidence that it’s just dense material that has clumped up, like an area rug on a slippery floor, and WR-18 is not in fact a runaway star heedlessly barging into molecular clouds.
This image is cropped from a 2-panel mosaic.
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