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Astronomers at the University of Warwick said this week that they now have the first direct evidence that white dwarf stars – stars at an advanced stage of their evolution – end up solidifying into crystals. This idea has been around for decades, but now new observations are behind it. The astronomers who conducted this study say that our skies must be filled with these white crystal dwarfs. They also point out that – long after they have swollen like a red giant and swallowed the Earth – our sun is destined to become a white crystal dwarf, too, billions of years from now.
The new study – led by Pier-Emmanuel Tremblay – was published on January 9, 2019 in peer-reviewed journal Nature
Current models of our home galaxy, the Milky Way, suggest that our galaxy alone currently contains about 10 billion white dwarfs. They are the warm and dense remnants of long dead stars, essentially stellar cores, left behind after a star exhausted its fuel supply and blew its gas and dust volume into space.
These exotic objects mark the final stage of evolution for most of the stars in the universe, including our sun.
According to the new study, the oldest white dwarfs, almost the age of the galaxy in the Milky Way, are likely to be almost completely crystallized.
Astronomers selected 15,000 white dwarf candidates in about 300 light-years from Earth from observations made by the European Space Agency's Gaia satellite. They then analyzed Gaia's data on the luminosities and colors of the stars. The analysis showed that white dwarfs have a solid oxygen and carbon core. This is due, astronomers say, to a phase transition during its life cycle similar to that of water that turns into ice but at much higher temperatures.
The work showed that these white dwarfs are probably older than previously believed. The astronomers' statement explained:
They identified an accumulation, an excess in the number of stars in specific colors and luminosities that do not correspond to any mass or age. When compared to evolutionary star models, the buildup coincides strongly with the phase in its development in which the latent heat is predicted to be released in large quantities, resulting in a deceleration of its cooling process. It is estimated that in some cases these stars have retarded their aging by up to 2 billion years, or 15% of the age of our galaxy.
Pier-Emmanuel Tremblay says:
This is the first direct evidence that white dwarfs crystallize, or transition from liquid to solid. It was foreseen 50 years ago that we should observe an accumulation in the number of white dwarfs in certain luminosities and colors due to the crystallization and only now this was observed.
All white dwarfs will crystallize at some point in their evolution, although more massive white dwarfs will pass through the process earlier. That means that billions of white dwarfs in our galaxy have completed the process and are essentially crystal balls in the sky.
The sun itself will become a white crystal dwarf in about 10 billion years.
Conclusion: Astronomers now have the first direct evidence – from ESA's Gaia satellite – that white dwarf stars form crystal nuclei.
Source: Nucleus of crystallization and stacking in the cooling sequence of developing white dwarfs
Via University Warwick