One day our sun will so­lid­ify into a gi­ant crys­tal orb

Daily Sabah (Turkey) - - Lifestyle -

OUR sun and bil­lions of stars just like it are headed for a strange, cold des­tiny. New re­search sug­gests that long af­ter our roil­ing, boil­ing life-giv­ing star runs out of fuel it will slowly form a cold, dead, su­per-dense crys­tal sphere about the size of the Earth that will linger like a translu­cent tomb­stone for close to eter­nity.

“In tens of bil­lions of years from now the uni­verse will be made largely of dense crys­tal spheres,” said Pier-Em­manuel Tremblay, an as­tro­physi­cist at the Univer­sity of War­wick in Coventry, Eng­land, who led the work pub­lished this week in the jour­nal Na­ture. “In the fu­ture, these ob­jects will be com­pletely dom­i­nant.”

To come to this con­clu­sion, the re­searchers used data col­lected by the European Space Agency’s Gaia te­le­scope to an­a­lyze the color and bright­ness of 15,000 white dwarf stars within 300 light-years of Earth.

White dwarf stars are among the old­est ob­jects in the uni­verse, and rep­re­sent one of the fi­nal life phases of stars like the sun.

Cur­rently, our sun is about half way through the main se­quence phase, which means it cre­ates en­ergy by fus­ing hy­dro­gen into he­lium in its core.

In about 5 bil­lion to 6 bil­lion years it will run out of hy­dro­gen. Then its core will shrink and the rest of the star will puff up into a rel­a­tively short-lived red gi­ant phase which will last about 500 mil­lion to a bil­lion years be­fore it con­tracts once again.

Af­ter this con­trac­tion the star can still cre­ate en­ergy by fus­ing he­lium to cre­ate car­bon and oxy­gen, Tremblay said.

How­ever, this form of en­ergy gen­er­a­tion burns quickly and will only last for a few bil­lion years.

When that process comes to an end, the sun will en­ter the white dwarf stage, which is es­sen­tially a re­tired star made up pri­mar­ily of oxy­gen and car­bon gas.

White dwarf stars start off ex­tremely hot, but they no longer gen­er­ate their own en­ergy. And while they ini­tially ra­di­ate enough heat that we can see them in our tele­scopes, they slowly lose their en­ergy over bil­lions of years.

“It’s like tak­ing a hot coal out of a fire and let­ting it cool off into the night,” said JJ Her­mes, an astronomer at Bos­ton Univer­sity who worked on the study.

It is not pos­si­ble to ob­serve crys­tal struc­tures in white dwarf stars di­rectly, but it is pos­si­ble to see ev­i­dence of the crys­tal­liza­tion process, the au­thors said.

If the stars did not crys­tal­lize they would cool at a steady rate, go­ing from blue to or­ange to red and los­ing bright­ness along a smooth slope. But that’s not what the Gaia data show.

In­stead, the au­thors found an ex­cess num­ber of white dwarf stars in a cer­tain color and bright­ness re­gion.

This pileup, or traf­fic jam in the data sug­gests that at around the same point in the cool­ing process, the stars sim­ply stop get­ting colder.

“We see them sit­ting there for hun­dreds of mil­lions and even bil­lions of years when they should be cool­ing on a much shorter time scale,” Her­mes said.

The only ex­pla­na­tion for this is that these stars have an ex­tra en­ergy source, said Tremblay.

Al­though the star is no longer gen­er­at­ing its own nu­clear en­ergy, it turns out that when mat­ter crys­tal­lizes from a liq­uid into a solid it re­leases en­ergy.

You can see this when wa­ter goes from a liq­uid to a solid in the freezer, Her­mes ex­plained. 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.

Once the crys­tal ar­range­ment is in place, the ice will con­tinue to cool at a more or less steady rate un­til it reaches the same tem­per­a­ture as the en­vi­ron­ment in the freezer.

The same thing is hap­pen­ing in cores of these white dwarf stars ex­cept over a much longer time pe­riod, the au­thors said. As the oxy­gen and car­bon in the star crys­tal­lize, they re­lease heat, caus­ing the star to stall its cool­ing for roughly 2 bil­lion years.

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.

The new find­ing sug­gests that not only is that en­ergy de­tectable, but it is at the up­per end of pre­dicted es­ti­mates by the­o­reti­cians, he said.

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 when the process is com­plete they be­come what are known as black dwarfs - cold crys­tal spheres that are not de­tectable with our tele­scopes be­cause they don’t emit en­ergy.

One day in the far-dis­tant fu­ture, Tremblay said, 97 per­cent of stars in the uni­verse will meet this fate.

Peo­ple gather as they wait for the sun to go down and the ap­pear­ance of the “Blood moon” in Ber­lin, July 27, 2018.

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