Thousands of white dwarf stars are turning into crystals

Thousands of white dwarf stars are turning into crystals
© University of Warwick/Mark Garlick

Thousands of white dwarf stars in our sky are solidifying into crystals, and the first direct evidence has been observed by astronomers at the University of Warwick.

This is the first observation of white dwarf stars turning into crystals. Dr Pier-Emmanuel Tremblay from the University of Warwick’s Department of Physics, said: “This is the first direct evidence that white dwarfs crystallise, or transition from liquid to solid. It was predicted fifty years ago that we should observe a pile-up in the number of white dwarfs at certain luminosities and colours due to crystallisation and only now this has been observed.”

White dwarf stars

White dwarf stars are some of the oldest stellar objects in the universe and have a predictable lifecycle, which allows astronomers to use them to estimate the ages of neighbouring stars with a high degree of accuracy.

Dead remnants of white dwarf stars have a core of solid oxygen and carbon. This is due to a phase transition during their lifecycle similar to water turning into ice, but at higher temperatures. These observations mean that they are potentially billions of years older than astronomers previously thought.

Skies filled with crystals

Crystallisation, the process of a material becoming a solid state in which atoms form an ordered structure. Atoms are packed so densely in the cores of white dwarf stars that the electrons become unbound and leave a conducting electron gas governed by quantum physics, and positively charged nuclei in a fluid form. The core cools down to about 10 million degrees, and the fluid begins to solidify, forming a metallic core with a mantle enhanced in carbon.

Tremblay added: “All white dwarfs will crystallise at some point in their evolution, although more massive white dwarfs go through the process sooner. This means that billions of white dwarfs in our galaxy have already completed the process and are essentially crystal spheres in the sky. The Sun itself will become a crystal white dwarf in about 10 billion years.”

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