Science

SNAPSHOT: First Direct Evidence Stars Like Our Sun Turn Into Crystals

SNAPSHOT: First Direct Evidence Stars Like Our Sun Turn Into Crystals”

Astronomers at the University of Warwick used Gaia's observations of hundreds of thousands of stars to prove that white dwarves, or the star corpses left after the red giant phase, crystallize. And because white dwarfs are among our cosmos' oldest stellar objects, with predictable life stages, astronomers often use them as "clocks" to date surrounding groups of stars. The work verified earlier predictions that such a catalog of white dwarf stars would reveal a number in the slow process of turning from what is essentially a liquid form to a solid state. If you were keeping track with a thermometer, you would find that the temperature of water stalls at zero degrees Celsius for a bit - the exact time that the H20 molecules are rearranging themselves into the crystal structure of ice.

They are the remaining cores of red giants after these huge stars have died and shed their outer layers and are constantly cooling as they release their stored up heat over the course of billions of years. The core is then formed of a crystallized metallic oxygen interior, with a carbon enhanced mantle. The data found a "pile-up", or a rather larger number of white dwarfs with "specific colors and luminosities that do not correspond to any single mass or age".

The team in Warwick studied 15,000 white dwarf candidates within around 300 light years of Earth and measured their colour and luminosity for clues about their composition. More massive stars cool down more rapidly and will reach the temperature at which crystallization happens in about one billion years. But as the star cools, that fluid solidifies and creates a metal core.

The Sun still has about five billion years before it becomes a white dwarf, and the astronomers estimate that it will take another five billion years after that to eventually cool down to a crystal sphere.

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

"Before Gaia we had 100-200 white dwarfs with precise distances and luminosities - and now we have 200,000", Tremblay said, giving the satellite the bulk of the credit for the research team's discovery.

"Not only do we have evidence of heat release upon solidification, but considerably more energy release is needed to explain the observations", said Tremblay. "This will push the carbon upwards, and that separation will release gravitational energy". At some time in their evolution, all white dwarfs will crystallize with more massive ones dying faster than the small ones.

"It's exciting how scanning stars across the sky and measuring their properties can lead to evidence of plasma phenomena in matter so dense that cannot be tested in the laboratory".



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