From nursery rhymes to poetry, stars have long been referred to as diamonds and crystals in the night sky – and, in some cases, this might not be far from the truth.
In a paper released this month, University of Southern Queensland PhD student Alexander Venner and a team of international scientists have observed a white dwarf star in the process of crystallisation.
A remnant of a long-dead star, white dwarfs undergo a process where their inner cores crystallise over time – a process which had long been theorised but only recently observed.
“Once a star like the Sun depletes its hydrogen source, which fuels its nuclear fusion, it continues on by fusing heavier elements like helium,” Mr Venner said.
“However, once the core is dominated by carbon, the fusion process cannot continue.
“This causes the star to explode, leaving behind a carbon and oxygen plasma core known as a white dwarf.
“The white dwarf is initially very hot, but as it cools, the atoms in the plasma core begin to stick together, forming grains of crystals.
“Because the pressure is much higher than on Earth, it forms a crystallised solid unlike any we would see here – one which is different to a diamond.”
In a scientific first, the team have been able to constrain the age of this crystallising white dwarf through its association with the three other stars in its system.
“My focus was on studying these other stars in the system and trying to constrain the amount of time since the system first formed,” Mr Venner said.
“By combining those two factors, we hoped to determine how long the white dwarf had been undergoing crystallisation and if this process had caused a cooling delay.
“In the end, we were a little short of statistical significance, but our findings were consistent with theoretical models that predict crystallisation causes a billion-year cooling delay.”
Mr Venner said white dwarfs are important celestial models, creating conditions that are impossible to simulate on Earth.
“Being able to observe these stellar laboratories, which occur in the sky around us, gives us insight into extreme particle physics,” he said.
“It allows us to have a greater understanding of what is happening within the star’s interior, something which would be otherwise inaccessible.”
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