In the late 1980s or early ’90s something changed, though. The star started getting hotter… a lot hotter. It went from about 21,000° C in 1980 (much hotter than the Sun’s 5500°) to a face-melting 60,000° by 2002. At the same time it shrank in size — this was determined by carefully measuring spectra taken of its light. Astronomers think that it had what’s called a late thermal pulse, where gas under incredible pressure in a shell around its core underwent furious rates of fusion, heating the star up.
This extra light zapped the gas already blown out by the star, lighting it up, causing it glow literally like a neon sign. That is, electrons in the gas atoms jumped up in energy levels, then emitted light when they dropped back down. That’s when it would’ve first been visible from Earth, making it the youngest planetary nebula ever seen.
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