In a process not unlike human aging, most stars entering the final chapter of their lives tend to slowly shrink and turn white. Astronomers call these cold, dense star shells white dwarfs , and unlike humans, this stage can last for billions of years.
Now, new research published in the journal Nature, argues that the white dwarf may be the beginning of a new and beautiful metamorphosis: it will end up becoming a cosmic crystal gem 200,000 times denser than Earth.
In studying more than 15,000 known white dwarfs around the Milky Way, a team of astronomers from the University of Warwick (UK) concluded that dying stars turn into luminous crystal orbs before disappearing.
White dwarfs can linger for billions of years before fading and dimming forever, but this is not the end of the story. Using observations from the European Gaia mission, which is currently making precise measurements of stars in our galaxy, researchers at the University of Warwick have uncovered a white dwarf secret that has remained hidden until now.
Crystal dwarf
Shortly after forming, white dwarfs are extremely hot. During the billions of years after their formation, white dwarfs slowly cool and, at a certain point, the oxygen and carbon they contain go through a phase transition, similar to the freezing of liquid water and conversion to ice. solid -which slows down the aging process-, only at much more extreme temperatures and pressures, solidifying and forming a huge crystal.
“All white dwarfs will crystallize at some point in their evolution, although more white dwarfs will go through the process sooner,” said Pier-Emmanuel Tremblay, from the Department of Physics at the University of Warwick and leader of the study. “This means that billions of white dwarfs in our galaxy have already completed the process and are essentially crystal spheres in the sky. The sun itself will turn into a crystal white dwarf in about 10 billion years .”
The researchers discovered that some of these stars had extended their lifespan up to 2 billion years.
“This is the first direct evidence that white dwarfs crystallize, or transition from liquid to solid,” added Tremblay. “Fifty years ago it was predicted that we should observe an increase in the number of white dwarfs in certain luminosities and colors due to crystallization, but this has not been observed until now .”
Crystallized white dwarfs aren’t just a stellar curiosity. As the material of the white star crystallizes, its material is ordered at a quantum level, the nuclei align themselves like a 3D lattice that creates a metallic oxygen core and a carbon-enriched outer shell.
So, after stars like our sun die, they still have stories to tell. All white dwarfs will go through this crystallization phase, adorning the galaxy with huge diamond-shaped stellar debris.
If that’s the case, the known white dwarfs may be billions of years older than previously thought. This complicates an already mysterious chronology, as scientists are not sure how long a dying star can remain as a white dwarf before it stops emitting light and heat altogether, thus becoming what some researchers call a “black dwarf.” “ . This theoretical end point of stellar evolution has never been observed.
Referencia: Core crystallization and pile-up in the cooling sequence of evolving white dwarfs. Pier-Emmanuel Tremblay, Gilles Fontaine, Nicola Pietro Gentile Fusillo, Bart H. Dunlap, Boris T. Gänsicke, Mark A. Hollands, J. J. Hermes, Thomas R. Marsh, Elena Cukanovaite & Tim Cunningham. Nature volume 565, pages202–205 (2019) DOI: https://doi.org/10.1038/s41586-018-0791-x
Crédito imagen: University of Warwick/Mark Garlick
