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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 in an advanced stage of their evolution – eventually solidify into crystals. That idea has existed for decades, but now new observations confirm this. 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 swelling up like a red giant and engulfing the Earth – our sun is destined to become a white crystal dwarf, even in billions of years.
The new study – conducted by Pier-Emmanuel Tremblay – was published on January 9, 2019 in the peer-reviewed journal Nature
The current models of our home galaxy, the Milky Way, suggest the our galaxy currently contains only about 10 billion white dwarfs. They are the hot and dense remains of dead stars for a long time, essentially star nuclei, left behind after a star has exhausted its fuel reserve and detonated its mass of gas and dust 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 same age as the Milky Way galaxy, will probably already be almost completely crystalline.
Astronomers selected 15,000 white dwarf candidates within about 300 light years from Earth from observations made by the Gaia satellite of the European Space Agency. They then analyzed Gaia's data on luminosity and the colors of the stars. The analysis showed that white dwarfs have a nucleus of solid oxygen and carbon. This is due, say astronomers, to a phase transition during their life cycle, similar to water that turns into ice but at much higher temperatures.
The work has shown that these white dwarfs are probably older than previously believed. The astronomers' statement explained:
They identified a pile-up, an excess in the number of stars with specific colors and luminosities that do not correspond to any single mass or age. Compared with the evolutionary models of the stars, the accumulation strongly coincides with the phase of their development in which it is expected that the latent heat is released in large quantities, with a consequent slowing down of their cooling process. It is estimated that in some cases these stars have slowed down their aging by 2 billion years, or 15% of the age of our galaxy.
Pier-Emmanuel Tremblay said:
This is the first direct evidence that white dwarfs crystallize or pass from liquid to solid. It was predicted 50 years ago that we should observe an accumulation in the number of white dwarfs at certain luminances and colors due to crystallization and only now has this been observed.
All white dwarfs will crystallize at some point in their evolution even if the most massive white dwarfs cross the process first. 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 white crystal dwarf in about 10 billion years.
Conclusion: astronomers now have the first direct evidence – from the Gaia satellite of the ESA – that white dwarf stars form crystalline nuclei.
Source: Crystallization of the core and stacking in the cooling sequence of the evolving white dwarfs
Via University Warwick