Neutron stars are like cosmic pralines

Neutron stars are like cosmic pralines

Neutron stars, among the densest objects in the universe, are still a mystery to physicists. But a new theoretical analysis could explain the internal structures of these super dense celestial bodies.

A neutron star is the collapsed core of a supergiant star (10 to 25 times larger than our Sun) that has run out of fuel. The central region of the star, 1 to 3 times the mass of the Sun, collapses in on itself, pushing electrons and protons against each other under such pressure that they become neutrons.

The immense mass of a neutron star is concentrated into a ball the size of an average city. A single teaspoon of neutron star material would have a mass of around one trillion kilograms.

Located light years from Earth, neutron stars are difficult to study. And their extreme compactness is not reproducible in the laboratory. Thus, since their discovery 60 years ago, scientists have been trying to determine their internal structure.

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To describe the properties of neutron stars, physicists must use “equations of state” to model their various properties – from temperature to density.

Physicists at Goethe University Frankfurt in Germany have successfully added other crucial information to these equations in research published in the Astrophysical Journal Letters.

Researchers have developed over a million equations of state for neutron stars. The equations are established by data from theoretical nuclear physics and astronomical observations. And the results revealed surprising conclusions.

“Light” neutron stars – masses less than 1.7 times that of our Sun – have a soft mantle and a rigid core, while “heavy” neutron stars – masses greater than 1.7 times the solar mass – are the opposite, with a stiff mantle and a hard core. heart.

“This result is very interesting because it gives us a direct measure of the center compressibility of neutron stars,” says lead author and project leader Professor Luciano Rezzolla. “Neutron stars apparently behave a bit like chocolate pralines: light stars look like those chocolates that have a hazelnut in their center surrounded by soft chocolate, while heavy stars can be thought of more like those chocolates where a layer hard contains a soft filling.”

Sweet analogies aside, the research shows the power of computer simulations to model extreme conditions that are otherwise difficult to probe.

The team used an analysis of the speed of sound through their modeled neutron stars to arrive at their ideas. The speed at which sound waves travel through a material can tell scientists how stiff or soft the material is. Such analysis is used on Earth to explore the interior of our planet, in particular to find oil deposits.

Other previously unexplained properties of neutron stars have also been discovered by modeling the equations of state.

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Interestingly, the researchers found that, regardless of the star’s mass, these compact objects likely all have a radius of about 12 kilometers, making them roughly the size of the university’s hometown. researchers, Frankfurt.

“Our extensive numerical study allows us not only to make predictions for the radii and maximum masses of neutron stars, but also to set new limits on their deformability in binary systems, i.e. how much they deform each other through their gravitational fields,” says co-author Dr. Christian Ecker. “This information will become particularly important for identifying the unknown equation of state with future astronomical observations and detections of gravitational waves from merging stars.”

The structure and composition of neutron stars remain elusive, but advances like these allow us to probe the densest objects in the universe.

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