Floating Crystals Slow Stellar Aging. for Some Stars, This Can Delay Death by Billions of Years
taylorvich writes:
https://phys.org/news/2024-03-crystals-stellar-aging-stars-delay.html
In 2019, astronomers discovered a group of white dwarfs that mysteriously stopped cooling. These "forever-young" stars remain at a near-constant surface temperature for at least eight billion years-an incredible length of time, considering the universe is 13.8 billion years old.
Something is fueling these stars from within, but given that they had run out of their nuclear fuel source, scientists were unsure what could be keeping them shining so brightly. Our research, recently published in Nature, presents the solution to this conundrum.
Using information gathered by the Gaia space observatory of the European Space Agency, researchers discovered that some white dwarfs essentially stop cooling.
By studying how white dwarfs are distributed as a function of temperature (from hot to cold) in the Gaia data, astronomers noticed an accumulation of white dwarfs at intermediate temperatures. This indicates that some white dwarfs spend more time at these intermediate temperatures-eight billion years more than thought possible.
White dwarfs are weird. A mere teaspoon of material from their cores weighs several tons. Under such extreme densities, matter can behave strangely. Even though the interiors of white dwarfs are millions of degrees hot, the density is high enough that they can freeze into a solid state. They form crystals out of the carbon, oxygen and other elements present in their interiors.
The formation of these crystals normally starts at the center of the star, where density is highest. As the white dwarf cools down, more crystals are formed in successive layers until almost the whole star is completely solid.
However, this inside-out crystallization does not apply to all white dwarfs. We discovered that the heaviest elements present in white dwarfs are expelled from the crystals as they are formed, just as salt is expelled from ice crystals when seawater freezes.
The crystals become less dense than their surroundings, and float up like ice cubes in a glass of water. As the crystals do not stay in place, the core cannot simply freeze from the inside out.
The movements created by the floating crystals reshuffle the chemical layering inside the star. Gradually, the heaviest elements are transported toward the center. This releases a steady flow of gravitational energy that keeps the star shining at a near-constant temperature for billions of years.
More information: Simon Blouin, Buoyant crystals halt the cooling of white dwarf stars, Nature (2024). DOI: 10.1038/s41586-024-07102-y. www.nature.com/articles/s41586-024-07102-y
Read more of this story at SoylentNews.