Neutron stars are like cosmic bonbons

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

A neutron star is the collapsed core of a supergiant star (10-25 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 so much pressure that they become neutrons.

The immense mass of a neutron star is concentrated into a ball the size of your average city. A a single teaspoon of neutron star matter would have a mass of about a trillion kilograms.

Being light years from Earth, neutron stars are difficult to study. And its extreme compactness is not something that can be replicated in a laboratory. So ever since they were first discovered 60 years ago, scientists have been trying to puzzle out 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 the Goethe University of Frankfurt in Germany have successfully added more crucial information to these equations in the research. published in the Astrophysical Journal Letters.

The researchers developed more than a million equations of state for neutron stars. The equations are established using data from theoretical nuclear physics and astronomical observations. And the results revealed some surprising conclusions.

“Light” neutron stars (masses less than 1.7 times the mass of the Sun) have a soft mantle and a rigid core, while “heavy” neutron stars (mass greater than 1.7 times the mass of the Sun) they are opposite, with a rigid mantle and a rigid core. center.

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

Delicious analogies aside, the research shows the power of computer simulations to model extreme conditions that would otherwise be difficult to test.

The team used an analysis of the speed of sound through their modeled neutron stars to gain their insights. The speed with which sound waves propagate within a material can tell scientists how rigid or soft the matter is. Such analysis is used on Earth to explore the interior of our planet, including the search for 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 are likely around 12 kilometers in radius, making them about the size of the researchers’ university hometown of Frankfurt.

“Our extensive numerical study not only allows us to make predictions about the radii and maximum masses of neutron stars, but also to set new limits on their deformability in binary systems, that is, how strongly they distort each other through their gravitational fields”. explains co-author Dr. Christian Ecker. “These insights will be particularly important for identifying the unknown equation of state with future astronomical observations and gravitational wave detections of merged stars.”

The structure and composition of neutron stars remains elusive, but breakthroughs like these take us one step closer to probing the densest objects in the universe.


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