A white dwarf may look like the quiet endpoint of a star’s life, but its spectrum can contain evidence of a planetary system that once surrounded it. Among the most useful clues are absorption lines produced by calcium. Calcium should not remain visible for long in the atmospheres of many white dwarfs. The enormous surface … Read more

A white dwarf may look like the quiet ending of a planetary system. The star has exhausted its nuclear fuel, shed much of its outer material, and collapsed into a dense stellar remnant roughly comparable in size to Earth. Any planets, asteroids, and comets that once orbited the original star have already survived a period … Read more

A white dwarf should have an extraordinarily simple atmosphere. Its immense gravity pulls heavier elements downward, leaving the visible surface dominated mainly by hydrogen or helium. Elements such as calcium, magnesium, iron, and silicon should disappear beneath the photosphere relatively quickly. Yet astronomers repeatedly find white dwarfs whose spectra contain exactly these elements. They call … Read more