Wednesday, 16 January, 2019

New study suggests ancient stars form crystal cores

Earth's Sun Will Turn into a Pure Crystal Ball Before It Dies Before a white dwarf dies it turns into a crystal ball research suggests. Credit University of Warwick Mark Garlick
Sandy Nunez | 11 January, 2019, 21:13

The crystal spheres are made of carbon and oxygen under such high density their crystal structure will make them appear to be like a metal - although it is possible that diamonds may also form as the star cools.

Data captured by ESA's galaxy-mapping spacecraft Gaia has revealed for the first time how white dwarfs, the dead remnants of stars like our Sun, turn into solid spheres as the hot gas inside them cools down.

"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. "It was predicted fifty years ago that we should observe a pile-up in the number of white dwarfs at certain luminosities and colours due to crystallisation and only now this has been observed".

As temperatures cool, the white dwarf's liquid begins to solidify.

Massive stars in the Universe die out with a great explosion that we call Supernova. In the diagram, blue lines show the cooling sequence of white dwarfs with different masses - 0.6, 0.9, and 1.1 times the mass of the Sun, respectively - as predicted from theoretical models.

Many scientists thought it was likely that white dwarf stars would form crystals as they cooled, but there was disagreement about whether the energy released from the process would be detectable, Tremblay said.

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For the new study, the researchers looked at Gaia measurements of about 15,000 white dwarfs, all of which lie within 330 light-years of the sun. The information found a "pile-up", or a somewhat bigger number of white dwarfs with "specific colors and luminosities that do not correspond to any single mass or age".

"White dwarfs are traditionally used for age-dating of stellar populations such as clusters of stars, the outer disk, and the halo in our Milky Way", Dr. Tremblay said. "It is assessed that now and again these stars have slowed down their aging by as much as 2 billion years, or 15 percent of the age of our cosmic system".

But just as the water in your freezer continues to cool after it releases all its latent energy, white dwarfs eventually resume their cooling as well. And while they initially radiate enough heat that we can see them in our telescopes, they slowly lose their energy over billions of years.

"All white dwarfs will crystallise at some point in their evolution, although more massive white dwarfs go through the process sooner". As for our Sun, the researcher and his colleagues estimate that it will undergo the crystallization process in around 10 billion years, give or take.

"The sun itself will become a crystal white dwarf in about 10 billion years", added Dr Tremblay, reminding us that these crystals - although a new discovery - are the usual end for stars.