Published: Sun, January 13, 2019
Sci-tech | By April Francis

Spotted: Stars that became cold balls

Spotted: Stars that became cold balls

The crystal stars are called "White Dwarf Stars".

"We've made a large step forward in getting accurate ages for these cooler white dwarfs and therefore old stars of the Milky Way".

The astronomers selected 15,000 white dwarf candidates within around 300 light years of Earth from observations made by the Gaia satellite and analysed data on the stars' luminosities and colours.

For the first time, astronomers have observed the white dwarf stars slowly crystallising and turning into solid spheres. Using data from the ESA's Gaia satellite, an worldwide group of researchers claim to have found evidence that supports the theory that when massive white dwarf stars like our brilliant host (the Sun) burn out and die, they solidify into metallic crystals.

The crystallization of white dwarfs is similar to how water turns into ice only that the cosmic process involve higher temperatures. Therefore, gaining a greater understanding of how crystallization can stave off the cooling process, essentially making the stars appear younger than they really are, would help astronomers improve the accuracy of the white dwarf dating technique.

Tremblay said their studies suggested that white dwarfs stop their cooling by turning from liquid to almost 99 per cent solid over about 1.5 billion years. As the oxygen and carbon in the star crystallise, they release heat, causing the star to stall its cooling for roughly 2 billion years.

When stars die, they eventually become white dwarfs and new evidence has found that white dwarfs eventually crystallize over time, though larger stars turn to crystals sooner than smaller ones.

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. Before it begins to solidify and harden gradually, the sun will turn into a red giant, and from that moment it will begin to shrink down and turn into a white dwarf. Our sun is also expected to end its life in the same manner, crystallizing like a jewel in about 10 billion years.

"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.

Dr. Tremblay adds: "Not only do we have evidence of heat release upon solidification, but considerably more energy release is needed to explain the observations".

"White dwarfs are traditionally used for age-dating of stellar populations such as clusters of stars, the outer disc, and the halo in our Milky Way", said Pier-Emmanuel.

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

"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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