A cutaway showing an artist’s impression of a white dwarf after undergoing crystallisation. Image: University of Warwick/Mark Garlick
Astronomers have found the first direct evidence supporting a five-decade-old idea that white dwarfs, the compact, burned-out remnants of stars like our Sun, solidify into solid spheres of oxygen and carbon crystals as their cores slowly cool in the absence of nuclear fusion. This crystallisation, similar to water changing into ice but at much higher temperatures – about 10 million degrees Celsius – slows down the evolution of white dwarfs, making them appear up to two billion years younger than they actually are.
“This is the first direct evidence that white dwarfs crystallise, or transition from liquid to solid,” said Pier-Emmanuel Tremblay of the University of Warwick. “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.
“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 ...