One moment, please economics research paper Planetary nebulas form when a star uses up all of the hydrogen in its core--something that our own Sun will experience in about five billion years. When this happens, the star begins to cool and expand, increasing its radius by tens to hundreds of times its original size. The outer layers of the star are then carried away by stellar winds, which strip away material and leave behind the hot core. This core then continues to eject more layers in a much faster wind. Eventually, this creates the complex and filamentary shell of a planetary nebula. In time, the remnant will collapse to form a white dwarf star. 必須 2000文字以内 [bbs:youtube:(Youtubeの動画ID)]と書くとYoutubeの動画が貼れます。(例:[bbs:youtube:OQThUAQ0UN0])