Some of the nebulae exhibit a set of concentric rings like bull's-eyes, possibly indicating that the ejection process was episodic rather than continuous.
Some of the nebulae exhibit a set of concentric rings like bull's-eyes, possibly indicating that the ejection process was episodic rather than continuous.
有些星云显露出一组圆形标靶般的同心环结构，可能暗示喷发气壳的过程并不连贯。