At the end of its life, our Sun could end up as a crystal—and physicists now have observational evidence to back up that theory.
Scientists have predicted that as white dwarfs cool, they can crystallise in a phase transition somewhat like water freezing into ice. New research from scientists in the UK, U.S., and Canada provides evidence of this transition in a survey of nearby white dwarfs. This is especially interesting to us because, as we’ve reported, scientists predict that our own Sun’s fate is to become a white dwarf.
White dwarfs are small, faint, and incredibly dense stars, the result of stars like the Sun running out of the fuel that powers their nuclear fusion. They have masses around that of the Sun but are only around the size of the Earth. They consist of a densely packed plasma of atoms and their electrons. The electrons are forbidden from sharing exact states by the rules of quantum mechanics, so they exert a pressure that keeps the stars from collapsing.
Though they’re plasmas, scientists have long predicted that these squished atoms should eventually crystallise, beginning at the stars’ centres. There’s been indirect observation of the crystallisation, but scientists now claim to have observed the process directly. They describe their findings in a paper published in Nature.
Models suggest that when white dwarfs crystallise, they release heat in order to enter the lower-energy phase, the way heat energy leaves water as it freezes into ice. This would slow down the star’s cooling, an effect that scientists can observe directly.
The team analysed a catalogue of 15,109 white dwarf candidates within 100 parsecs (326 light-years) of our Sun using data from the Gaia satellite. And indeed, they found a “pile-up” of stars at certain locations along a plot of colour versus brightness. That’s evidence of stars going through the phase transition from plasma to crystal, according to the paper.
Obviously, this is dependent on modelling, and perhaps other explanations could explain the data better. But it’s exciting stuff—this would imply that many white dwarfs could be older than scientists thought, since the crystallisation slows the ageing process.
And one day our Sun, too, may be a beautiful crystal ball. And we’ll be dead.
Featured illustration: University of Warwick/Mark Garlick