Image Credit: NASA / Spitzer / JPL-Caltech
White dwarfs, the slowly cooling remains of stars that have completed their life cycles, often seem to be the zombies of the night sky, devouring anything that happens to stray within their grasp. In an article that will be appearing in an upcoming issue of the Astrophysical Journal, astronomers Patrick Dufour, Mukremin Kilic and collaborators discuss a recently-discovered white dwarf that seems to have devoured a dwarf planet. Its name: "SDSS J073842.56+183509.6" (its nickname: 5877352363341268816. Seriously.)
White dwarfs have so much matter squeezed into such a little size that their pull of gravity is very strong. If you were to try and stand on the surface of the white dwarf remains of the sun, you would weigh one hundred thousand times more than you do now. So, if you weigh 150 pounds, on a white dwarf you would weigh 15 million pounds. Ouch.
That gravity is strong enough that the lightest element in a white dwarf's atmosphere will float to the top. The lightest element in the universe is hydrogen, and most white dwarfs have atmospheres of pure hydrogen. If you were to dump a heavy element, like iron, into a hydrogen-atmosphere ...