An analysis of the data collected by the ESA Gaia satellite showed that white dwarfs, remnants of stars like our Sun, begin to crystallize at some point in their life cycle, and many of them already have a core of solid oxygen and carbon. This process is similar to the transformation of water into ice, but proceeds at much higher temperatures. The results of the study are presented in the journal Nature.
The first direct evidence has been obtained that white dwarfs crystallize or transfer from a liquid to a solid state. These objects produce a certain brightness and color. Detection of hardened white dwarfs was predicted fifty years ago, but only today we were able to identify them.
-Pierre-Emmanuel Tramblay, lead author of the study from the University of Warwick (Great Britain)
White dwarfs are cosmic embers smoldering and cooling for billions of years, which remain after the red giants shed their outer layers. They are one of the oldest stars in the universe. Such objects are incredibly useful for astronomers, since their predictable life cycle makes it possible to use white dwarfs as space clocks for estimating the age of groups of neighboring stars with a high degree of accuracy, therefore understanding their evolution plays a crucial role in these calculations.
As part of the study, a team of astronomers selected 15,000 white dwarfs distant from Earth at a distance of up to 300 light years. Then they identified several groups in which there is a large number of stars with a certain color and luminosity, but at the same time with different masses and ages. Comparing the data obtained with the evolutionary models of luminaries, scientists have obtained convincing evidence of slowing cooling, that is, crystallization of the studied white dwarfs.
The fact is that if you look at the accumulation of such objects, then, as a rule, you can see a huge variation in their temperatures, since white dwarfs in them were formed at different times and, therefore, cooled differently. However, crystallization causes a noticeable slowdown in cooling and leads to the fact that at a certain temperature (crystallization temperature) there will be more white dwarfs in the group than others. It is assumed that in some cases, “dead” stars slow down their aging by 2 billion, that is, 15 percent of the age of our galaxy.
All white dwarfs crystallize at some point in their evolution, and the more massive of them pass through this process earlier. This means that thousands of white dwarfs in the Milky Way are already essentially crystalline spheres in the sky. It expects the Sun in about 10 billion years.
-Pierre-Emmanuel Tremblay
Crystallization is the process of transition of a substance into a solid state, in which its atoms form an ordered structure. At extreme pressures in the nuclei of white dwarfs, the atoms are packed so tightly that their electrons become unbound, floating in a hot plasma. When the core is cooled to about 10 million degrees, enough energy is released to the “liquid” to solidify, forming a carbon-coated metal core.
We have made a big step forward in determining the exact age of cold and old white dwarfs living in the Milky Way. Thanks to the accurate measurements of “Gaia”, now we have not 200 white dwarfs with exactly known distances and luminosity, but more than 200 thousand.
-Pierre-Emmanuel Tremblé
A solid glowing crystal will remain after the death of the sun
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