The dying remnants of burnt-out stars slowly crystallise as they cool 鈥� and we have just seen the process in action for the first time.
When sun-like stars use up their fuel, they become dense white dwarf stars and continue to cool down over billions of years. Similar to how vapour turns into water then ice as the temperature drops, astronomers predict that white dwarfs鈥� gaseous cores will crystallise and eventually become solid.
This decrease in temperature should also alter their colour and brightness. White dwarf stars become dimmer as they solidify, and their colour will change from blue to orange, to red, and then finally black.
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The process was first predicted 50 years ago but we聽had failed to see signs of it happening because it occurs deep within the star. Now, with data on thousands of white dwarf stars collected by European Space Agency鈥檚 Gaia satellite, Pier-Emmanuel Tremblay at the University of Warwick, UK and his colleagues have found a phenomenon that can only be explained by crystallisation.
The team analysed over 15,000 white dwarfs within about 300 light years of the sun. They found a huge cluster of stars unusually exhibiting the same brightness and colour. These stars have vastly different ages and origins, so normally we would expect them to look dissimilar.
鈥淭here is no other explanation to it other than crystallisation,鈥� Tremblay says. Stars lower their internal temperature by shedding heat to the environment. When they cool down to a certain temperature and begin to crystallise, the around them functions like a sweater, delaying further cooling. That鈥檚 why thousands of them dwell in the same stage, he says.
This slowdown could mean that white dwarfs take one to two billion years longer than previously thought to solidify, says Tremblay.
Nature
