BEIJING, Jan. 7 (Xinhua) — According tomedia reports, the sun may appear to be a permanently burning gas ball, but one day it will die, which may sound depressing, especially for creatures that have lived on Earth for billions of years. But there is a bright side to the death of the sun. According to a study published in the January 2019 issue of the journal Nature, the dead sun will leave behind a glittering legacy: a giant crystal, but that’s not the kind of crystal you can find on a regular chandelier.
This artistic imagination shows a solidified white dwarf star, and perhaps the same process will happen in the future.
Before we discuss super-large star crystals, we first need to understand how stars like the sun survive and die.
From red star to white dwarf
The sun generates energy through the fusion of atoms, and its enormous gravitational pull squeezes the hydrogen atoms in the core of a star, coalesces into helium atoms, and in the process releases a lot of energy, pushing outwards, maintaining a good balance. As long as there is enough hydrogen fuel to support this process, the size and temperature of the core remain the same (approximately 15 million Kelvin). The energy generated by nuclear fusion radiates throughout the solar system, eventually giving birth to the evolution of life on Earth’s habitable planet. During the life cycle experienced by the sun, this hydrogen-burning phase lasts about 90 percent of the time, and this lifetime star is called the “main sequence star.” Today, the sun’s main sequence has been 4.5 billion years — about half of its life.
What happens when the hydrogen atom runs out? Euphemistically, things get a little crazy. Without the outward pressure of the energy generated by the fusion hydrogen, the sun’s gravity would overwhelm its core and be squeezed into a smaller space, with a temperature increase tenfold. But that’s okay, the heavier helium nuclei will begin to gather, again generating outward pressure to maintain balance. This is expected to happen in about 5 billion years, marked by a sudden eruption of energy called a helium flash. During helium fusion, carbon and oxygen form and the core temperature rises again.
Soon, even heavier elements began to converge, making the sun look a little worse overall because of material consumption. It will begin to expand, violent solar winds will sweep through interstellar space, and the sun’s outer layer will begin to peel away. However, the mass of the sun is not enough to erupt called a supernova, but to become a red giant. It could expand beyond Earth’s orbit, scorching our planet.
At the end of the red giant, the remaining gas in the sun’s outer layer is sent into space by the solar wind and ionised into the solar plasma, creating a beautiful planetary nebula. The nebula is rich in newly formed heavy elements that will continue to be used to produce the next generation of stars and planets. When the outer layer is stripped, the only remaining will be the core of a hot star known as a white dwarf. It is a small, dense star that will cool and darken over billions of years, proving the sun’s former status.
White dwarfs will go out and darken forever in billions of years, but this is not the end of the story. Using observations from the European Gaia mission, researchers at the University of Warwick in the UK stumbled upon a long-hidden white dwarf star.
Crystal White Dwarf
Shortly after its formation, the white dwarf became very hot, ejeclated the intense energy that had previously been in the core of the main sequence star. Over the billions of years after its formation, the white dwarf will cool down and, at some point, its internal oxygen and carbon will undergo a phase-in change — similar to liquid water freezing into solid ice. Only at very extreme temperatures and pressures do carbon and oxygen cure to form a giant crystal.
“All white dwarfs crystallize at some point in their evolution, and larger white dwarfs go through this process more quickly,” study leader Pierre-Emmanuel Tremblay of the Department of Physics at the University of Warwick said in a press release. It’s essentially a crystal ball in the sky. In about 10 billion years, the sun itself will become a white dwarf. “
Trumble’s team analyzed observations from the Gaia mission, measuring the brightness and color of 15,000 white dwarfs within 300 light-years of Earth, and observing an excessive number (or “accumulation”) of stars of some color and brightness. They realized that the group of white dwarfs represented a similar phase in the evolution of the star, which had conditions suitable for crystallization phase change, which could lead to a delay in cooling, which slowed the aging process of the star. The researchers also found that some of these stars had a 2 billion-year longer lifespan.
“This is the first direct evidence of white dwarf crystallization, or liquid conversion to solids,” Mr. Tremblay said in a statement. “
Crystalline white dwarfs are more than just a star. Their quantum composition is different from anything we can rebuild in the lab. When the white dwarf material crystallizes, its material becomes orderly at the quantum level, with the nuclei arranged into a three-dimensional lattice, forming a metal oxygen core and a carbon-rich outer layer.
So after the death of stars like the sun, their story is not over. All white dwarfs go through this crystallization phase, leaving behind a large number of diamond-like star wrecks in the galaxy. (Any day)