White dwarfs are the dense cores left behind when stars exhaust their fuel and collapse. They are Earth-sized stellar embers weighing typically half as much as the Sun, made up of carbon-oxygen cores with surface layers of helium and hydrogen. Using far-ultraviolet data from the NASA/ESA Hubble Space Telescope, astronomers have discovered atmospheric carbon in the long-known ultramassive white dwarf WD 0525+526, and also found that the total masses...
