First Direct Evidence Of White Dwarf Stars Turning Into Crystals

They identified a pile-up, an excess in the number of stars at specific colors and luminosities that do not correspond to any single mass or age. When compared to evolutionary models of stars, the pile-up strongly coincides to the phase in their development in which latent heat is predicted to be released in large amounts, resulting in a slowing down of their cooling process. It is estimated that in some cases these stars have slowed down their aging by as much as 2 billion years, or 15 percent of the age of our galaxy.

“This is the first direct evidence that white dwarfs crystallise, or transition from liquid to solid,” Dr Pier-Emmanuel Tremblay from the University of Warwick’s Department of Physics, said in a press release.

“It was predicted fifty years ago that we should observe a pile-up in the number of white dwarfs at certain luminosities and colors due to crystallization and only now this has been observed.”

“All white dwarfs will crystallize 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.”

Crystallisation is the process of a material becoming a solid state, in which its atoms form an ordered structure. Under the extreme pressures in white dwarf cores, atoms are packed so densely that their electrons become unbound, leaving a conducting electron gas governed by quantum physics, and positively charged nuclei in a fluid form. When the core cools down to about 10 million degrees, enough energy has been released that the fluid begins to solidify, forming a metallic core at its heart with a mantle enhanced in carbon.

“Not only do we have evidence of heat release upon solidification, but considerably more energy release is needed to explain the observations. We believe this is due to the oxygen crystallizing first and then sinking to the core, a process similar to sedimentation on a river bed on Earth,” Dr Tremblay said.

“This will push the carbon upwards, and that separation will release gravitational energy.

“We’ve made a large step forward in getting accurate ages for these cooler white dwarfs and therefore old stars of the Milky Way.

Tremblay added that before Gaia we had 100-200 white dwarfs with precise distances and luminosities – and now we have 200,000. This experiment on ultra-dense matter is something that simply cannot be performed in any laboratory on Earth.