Astronomers observe white dwarf stars solidifying into crystals

Cristina Cross
January 13, 2019

White dwarf stars are some of the oldest stellar objects in the universe.

The Sun might die in 10 billion years' time, and when it does, according to scientists, it will turn into a "crystal ball".

Tremblay and his colleagues selected 15,000 white dwarf stars within 300 light years of Earth and analysed their luminosities and colours - or measures of energy emissions and temperatures - using the European Space Agency's Gaia telescope. "We believe this is due to the oxygen crystallizing first and then sinking to the core, a process similar to sedimentation on a riverbed on Earth".

"We could visualise crystallised white dwarfs as giant balls of solid oxygen and carbon, with only tiny amounts of other residual elements", Pier Emmanuel Tremblay, assistant professor of astronomy at Warwick who led the study, told The Telegraph.

They distinguished a heap up, an excess in the number of stars at explicit colors and luminosities that don't compare to any single mass or age.

Like all stars, our sun began in a nebula, where gas and dust collapsed on itself in a flurry of cosmic friction. Astronomers from the University of Warwick say they've found the first direct evidence that white dwarf stars - the dense, stellar corpses of stars like our sun - can crystallize, or turn from a liquid into a solid.

However, the death of a red dwarf and its subsequent transformation into a white dwarf does not mark the end of its evolutionary journey. This is due to a phase transition during their lifecycle similar to water turning into ice, but at higher temperatures. The process really kicks into gear when a white-dwarf interior cools down to about 18 million degrees Fahrenheit (10 million degrees Celsius), the researchers said.

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If the stars did not crystallise they would cool at a steady rate, going from blue to orange to red and losing brightness along a smooth slope.

"We saw a pile-up of white dwarfs of certain colors and luminosities that were otherwise not linked together in terms of their evolution", Dr. Tremblay explained.

ESA's Gaia satellite has observed dead stars that are the first direct evidence of an extraordinary phenomenon predicted 50 years ago.

That, in turn, has an impact on our understanding of the stellar groupings these white dwarfs are a part of.

"All white dwarfs will crystallise at some point in their evolution, although more massive white dwarfs go through the process sooner".

"We will now have to develop better crystallisation models to get more accurate estimates of the ages of these systems".

Not all white dwarfs crystallize at the same pace. The astronomers realized that this pile-up was not a distinct population of white dwarfs, but the effect of the cooling and crystallization of the originally hot matter inside the star's core.

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