Neutron stars, discovered more than 60 years ago, are formed when a supermassive star collapses. They are compact and dense, and physicists liken them to the mass of the sun being compressed into a sphere the size of a large city.

These extreme conditions can’t be replicated in a laboratory, so scientists have had their work cut out trying to understand exactly what makes up a neutron star.

A team at Goethe University in Frankfurt, Germany, using hundreds of thousands of ‘equations of state’ to describe the stars’ properties, made the discovery which gave them this yummy new point of reference – chocolate pralines!

‘Light’ neutron stars (with masses smaller than approximately 1.7 solar masses) seem to have a soft layer and a stiff core, whereas ‘heavy’ neutron stars (with masses larger than 1.7 solar masses) have a stiff layer and soft core.

The key equation behind the finding was the speed of sound, which measures how fast sound waves bounce around within an object. This will depend on how stiff or soft matter is, and on Earth is used to explore the inside of the planet and discover oil deposits.

Professor Luciano Rezzolla, who led the university group, said: “This result is very interesting because it gives us a direct measure of how compressible the centre of neutron stars can be. Neutron stars apparently behave a bit like chocolate pralines: light stars resemble those chocolates that have a hazelnut in their centre surrounded by soft chocolate, whereas heavy stars can be considered more like those chocolates where a hard layer contains a soft filling.”

Despite the ‘sweet satisfaction’ of these latest findings, the scientists say neutron stars still hold many mysteries, including their exact structure and composition.