A ring nebula is a type of planetary nebula characterized by its doughnut-like shape, which results from the ejected outer layers of a dying star. These structures are formed when a medium-mass star exhausts its nuclear fuel and sheds its outer envelope, revealing the hot core that ionizes the surrounding gas and dust, causing it to glow. Ring nebulae are key indicators of the late stages of stellar evolution, providing insight into the processes involved in stellar death.
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