Habitable huddle

摘要

One reason it seems so crazy is the way white dwarfs are born. After a sun-like star has burned the hydrogen fuel at its core, it balloons into a monstrous red giant more than 100 times wider than the sun. It engulfs and destroys any nearby planets, a fate that will befall Mercury and possibly Venus and Earth in about 7 billion years. Within another billion years the red giant sheds its outer layers of gas to form a glowing planetary nebula. The exposed hot, dense core is a white dwarf.