Life isn’t exactly like a box of chocolates, but there seems to be something in it. Some of the densest objects in the universe, neutron stars can have structures very similar to chocolate candies, with sticky or hard centers. What kind of particle configurations these centers consist of is still unknown, but the new theoretical work that reveals this surprising result may bring us one step closer to understanding the strange interior of these dead stars and the possible wild excesses in our universe.

Neutron stars are amazing. If we think of black holes as objects with enormous (if not infinite) matter density, neutron stars rank second in the universe’s highest density award. When the fusion material in the core of a star whose mass is approximately 8 to 30 times that of the Sun is depleted, it is no longer supported by the heat pressure from the outside, allowing the core to collapse under the force of gravity like the gas envelope that surrounds it. goes away. into space

The resulting neutron star has a reduced mass of about 2.3 times that of the Sun, but is compressed into a sphere only 20 kilometers (12 mi) in diameter. This thing is INTENSE with capital letters – and scientists are dying to know exactly what happens to matter under such incredible pressure.

Some studies suggest that the beans clump together until they form pasta-like shapes. Others suggest that even deeper into the star, the pressure becomes so extreme that the atomic nucleus ceases to exist altogether and turns into a “soup” of quark matter. Now, theoretical physicists led by Luciano Rezzola of Goethe University in Germany have discovered how neutron stars can be like chocolates with different fillings.

The team combined theoretical nuclear physics and astrophysical observations to develop more than a million “equations of state.” These are equations that relate the pressure, temperature and volume of a particular system, in this case a neutron star. Using these, the team developed a scale-dependent description of the speed of sound in neutron stars. And this is where it gets interesting. The speed of sound in a given object, whether star or planet, can reveal the nature of its internal environment.

Just as seismic waves on Earth and Mars propagate differently through materials of different densities, revealing structures and layers, sound waves bouncing around stars can reveal what’s going on inside them. When the team used the equations of state to study the speed of sound in neutron stars, their structures were not the same in all directions. Instead, neutron stars at the lower end of the mass range of less than 1.7 solar masses had soft covers and more solid cores, while those with masses greater than 1.7 solar masses had hard covers and soft cores.

“This result is very interesting because it gives us a direct measure of how compressible the center of neutron stars is,” says Rezzolla.

“Neutron stars seem to behave a bit like chocolate pralines: light stars look like chocolates with hazelnuts surrounded by soft chocolate in the center, while heavy stars can be thought of more like chocolates where the hard layer contains the soft filling”.

This seems consistent with both nuclear paste and quark soup interpretations of neutron star interiors, but it also provides new insights that could help model neutron stars across a range of masses in future studies. This could also explain why all neutron stars, regardless of their mass, have the same diameter, roughly about 20 kilometers.

“Our large-scale numerical work allows us not only to make predictions about the radii and maximum masses of neutron stars, but also to set new limits on their deformability in binary systems, namely how much they distort each other with their gravitational fields,” says physicist Christian Ecker of Goethe University.

“These insights will be particularly important for pinpointing the unknown equation of state through future astronomical observations and detecting gravitational waves from merging stars.” Source