The European Space Agency's satellite discovers a completely new astrophysical phenomenon related to white dwarfs

This pioneering discovery is based on data collected by the Gaia satellite (Global Astrophysical Interferometer for Astrophysics) From the European Space Agency (ESA), a satellite whose main purpose is to obtain measurements of the positions, distances and movements of stars and other celestial bodies (astrometry).

The satellite was launched into space on December 19, 2013 In theory, its mission was supposed to last only five years, but taking into account its enormous results, it was decided to extend it several times, currently theoretically, until 2025.

What Gaia detected was anomalous behavior in a population of white dwarfs. Essentially, the cooling process in these stars stopped more than eight billion years ago.

What is a white dwarf?

We've talked a lot about stars and their evolution. Depending on their size, stars go through different final stages. If the star's mass is more than 8 times the mass of the Sun, it could end its existence in a catastrophic supernova And brilliant, or it could collapse into a neutron star, or it could lead to a stellar black hole.

Conversely, if the mass of a star is less than 8 times the mass of the Sun, it cannot give rise to such amazing phenomena and become a white dwarf.It is a small star that resembles the Earth, with low luminosity, and its color tends to white, but its mass is similar to the mass of the Sun or even slightly larger than it. This means that the density of these stars is very high, as is their surface gravity.

In these stars, once hydrogen and helium are exhausted, nuclear fusion processes also end, because they are unable to trigger subsequent thermonuclear reactions. So, They do not have independent energy sources capable of counteracting gravitational collapseWith electron pressure being the only force preventing collapse.

But as the collapse continued, The stars inside it gradually cool until they are extinguished. In the cooling process, the dense plasma inside the star crystallizes and the star freezes.

Jaya discovered an anomaly

but, In 2019, Gaia noticed the presence of some white dwarfsInstead of gradually becoming extinct, Maintain their continued brilliance over a longer period than generally accepted evolutionary models assume.

for this reason, It was recently published in nature It is a study that presents a new theory for this phenomenonwhich, however, is based on behavior known to us on Earth.

According to researchers, in fact, During this crystallization process, a solid-liquid distillation mechanism is created It is operated by depletion of the solid phase of heavy impurities.

Basically, The plasma inside the starInstead of gradually solidifying from the inside out as a single mass, It forms dense solid crystals immersed in liquidwhich then tends to float to the surface.

This process is basically what we observe when we have liquid water ice Cube.

This behavior means that As the crystals move toward the star's surface, the heavier fluid moves inwardThis leads to thermal transport of dense material towards the center of the star, releasing gravitational energy to interrupt the star's cooling process for billions of years.

Why do some stars act this way?

According to this study, It appears that the different behavior of some stars is due to their different chemical composition. If the content of heavy elements differs, the behavior of the star in its final phase also differs.

this study This is especially important because white dwarfs are often used as indicators of the age of star clusters. Clearly, delayed cooling forces a revision of the model currently used to reconstruct the path of galaxy formation.

News reference:

Bédard, A., Blouin, S. & Cheng, S. Blooming crystals stop cooling of white dwarf stars. nature 627, 286-288 (2024). https://doi.org/10.1038/s41586-024-07102-y