Like most stars in the Milky Way galaxy, the sun will collapse into a white dwarf once it exhausts all its central nuclear fuel and lost its outer layers.

ESA's Gaia Spacecraft

In their new study published in the journal Nature, physicist Pier-Emmanuel Tremblay, from the University of Warwick in England, and colleagues looked at the data collected by the European Space Agency's Gaia spacecraft.

The space observatory was launched in 2013 to chart a 3D map of the Milky Way. The mission aims to study and monitor the position of more than 1 billion stars over the operational lifetime of the spacecraft.

Pileup

Tremblay and colleagues looked at Gaia measurements of about 15,000 white dwarf and found a pileup, an excess of white dwarfs whose colors and brightness are not associated with their age or mass.

Modeling revealed that this odd pileup was due to the crystallization of the white dwarf's interior that released heat to slow down the cooling of the white dwarfs.

"Using modelling, we infer that this pile-up arises from the release of latent heat as the cores of the white dwarfs crystallize," the researchers wrote in their study which was published on Jan. 9.

White Dwarf Crystallization

Crystallization is the process by which materials turn into a solid form in which the atoms are organized into a structure known as crystals.

The crystallization of white dwarfs is similar to how water turns into ice only that the cosmic process involve higher temperatures. The process results in white dwarfs with a core of crystallized oxygen and mantle dominated by carbon.

The astronomers said that their observation provides the first direct evidence that white dwarf stars would solidify into crystal.

"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," Tremblay explained.