字幕表 動画を再生する 英語字幕をプリント Planetary Nebula Survey Narrator (April Hobart, CXC): A planetary nebula is a phase of stellar evolution that the sun should experience several billion years from now, when it expands to become a red giant. It will then shed most of its outer layers, leaving behind a hot core that contracts to form a dense white dwarf star. A wind from the hot core will ram into the ejected atmosphere, creating beautiful, shell-like structures seen with optical telescopes. This gallery shows four planetary nebulas from the first systematic survey of such objects in the solar neighborhood made with NASA's Chandra X-ray Observatory. X-ray emission from Chandra is colored purple and optical emission from the Hubble Space Telescope is colored red, green and blue. The diffuse X-ray emission is caused by shock waves as the wind collides with the ejected atmosphere.