Article by: Andacs Robert Eugen, on 11 December 2022, at 10:02 am PST

Neutron stars, some of the densest objects in the Universe, can have a very chocolate-like structure, with a sticky or hard center. It is not yet known what kind of particle configurations these centers are made of, but the new theoretical work that revealed this surprising result could bring us one step closer to understanding these stars.

If we consider black holes as objects with immense (if not infinite) concentrations of matter, neutron stars earn second place in the list of the densest in the Universe. Theoretical physicists led by Luciano Rezzolla from Germany's Goethe University discovered how neutron stars could be like chocolates with different fillings.

The team combined theoretical nuclear physics and astrophysical observations to develop a set of more than a million equations. Using these, the team produced a scale-dependent description of the speed of sound in neutron stars.

The speed of sound in a given object, be it a star or a planet, can reveal the structure of its interior. When the team used the equations of state to study the speed of sound in neutron stars, their structures were not uniform.

"This result is very interesting because it gives us a direct measure of how fluid the center of neutron stars can be," says Rezzolla. "It seems that neutron stars behave a bit like chocolate pralines: light stars resemble those chocolates that have a hazelnut in the center surrounded by soft chocolate, while heavy stars can be thought of more like those chocolates where a hard layer contains a soft filling."