We already know which is the best natural factory for the most precious rare earths: a cosmic kilonova.

Neutron stars and the still-hypothetical quark stars, like black holes, are exciting objects. Astrophysics has developed so much in the last few decades that it can be done provide us with very valuable information about them, which encourages us to remain hopeful in the hope that cosmologists will get to know them better and help us understand their dynamics more accurately.

Neutron stars are formed when the outer layers of some star are ejected into the stellar medium, although only if the resulting object has a solar mass greater than 1.44, a value known as the Chandrasekhar limit, in honor of the Indian astrophysicist. goes. Who calculated it, the stellar remnant will collapse once again to give rise to one of these stars. Moments before a supernova occurs, the iron cores of giant stars are subjected to the enormous pressure of the upper layers and the constant action of gravitational contraction.

These processes trigger a mechanism of quantum nature that brings about very significant changes in the structure of matter, causing the iron in the stellar core to photodisintegrate. action of high energy photons, which produce gamma radiation. These photons manage to disintegrate the iron and helium in the star’s core, producing alpha particles, which are helium nuclei that lack their electron shells, and therefore, contain a positive electrical charge and neutrons. Are.

A kilonova is capable of synthesizing heavy elements, including rare earth elements.

The exotic process of neutron star formation continues to give rise to a mechanism called beta capture, which we are not going to discuss so as not to complicate the article. Importantly, we know that this causes the electrons in the iron atoms to interact with the protons in the nucleus, neutralizing their positive charge and producing more neutrons. The propagation of these latter particles has already begun.

During the formation of neutron stars, the initial matter, which was composed of protons, neutrons, and electrons, becomes composed only of neutrons because, as we have just seen, electrons and protons have interacted. through electronic capture To produce more neutrons. From that moment the star was no longer made of ordinary matter; It has transformed into a kind of giant crystal made only of neutrons.

However, once the star reaches this state we can ask ourselves what mechanism allows this ball of neutrons to withstand and counteract the pressure exerted by the relentless gravitational contraction. The phenomenon responsible for keeping the neutron star in equilibrium is the Pauli exclusion principle, which is an effect of quantum nature. This establishes that two fermions of the same quantum system cannot occupy the same quantum state.

Quarks, which are the elementary particles that make up the protons and neutrons of atomic nuclei, are fermions. And electrons too. What does it mean that there cannot be two fermions by simple guess? achieve the same quantum state And by understanding where the balance of neutron stars comes from, we can understand how the impossibility of two neutrons living in the same place generates the pressure necessary to keep the star in balance.

And this brings us to undoubtedly the most surprising characteristic of neutron stars: their density. The average radius of one of these objects is about ten kilometers, but its mass is much greater. For example, compared to stars found on the main sequence or even white dwarfs, neutron stars are very small, and cramming so much mass into such a small space would cause a cubic centimeter fragment to form a The neutron star weighs approximately, no more and no less, a billion tons.

We need everything we’ve reviewed so far to fully understand what happens next. When two neutron stars, a neutron star and a black hole, or a neutron star and a white dwarf collide, an extraordinary energetic cosmic event occurs. known as kilonova, As we have seen, neutron stars have a very high amount of matter and their density, so their energy is also very high.

An international team of scientists, in which Spanish astrophysicists from the Institute of Astrophysics of Andalusia (IAA-CSIC) participate, have discovered that kilonovae have the potential to produce some of the heavy chemical elements that we can find in the universe, such as That is, for example, rare earths or lanthanides. This specific group of chemical elements includes some metals that are elusive and whose names are suggestive such as neodymium, promethium, gadolinium, yttrium or scandium.

Some of them are relatively rare, and, moreover, they are not usually found in pure form in nature, but what makes them so special are their physicochemical properties. Their characteristics are beyond the reach of other elements of the periodic table, due to which they have been consolidated as a very valuable resource In many industries, especially electronics and renewable energy.

And they are involved, for example, in the manufacture of hybrid and electric car engines, batteries, catalysts, lasers, fiber optics, LCD panels and even wind turbines. The scientific article published by the astrophysicists responsible for this discovery is very interesting, so I suggest you read it if you want to delve deeper into this discovery. Before concluding this article, it is worth remembering that stellar nucleosynthesis can only trigger the formation of elements of the periodic table that are lighter than iron and the latter.

To produce chemical elements even heavier than iron, it requires the intervention of titanic amounts of energy that exist only in a few gigantic cosmic events. Kilonova is one of them. What allowed these astrophysicists to make this discovery gamma ray burst Which was observed on March 7, 2023 and was probably produced by the collision of two neutron stars located in a galaxy at a distance of about 950 million light years from Earth. Exciting, right?

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More information | CSIC

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