Neutron stars are a bit like chocolate bonbons

Photo: Peter Kiefer and Luciano Rizzola

Since their discovery more than 60 years ago, scientists have been trying to learn more about the interiors of so-called neutron stars—the collapsed cores of exhausted massive stars. Unfortunately, the extreme conditions of this stuff are hard to simulate in the lab.

Therefore, researchers rely on models in which various properties — such as density and temperature — are described using so-called equations of state. These equations attempt to describe the structure of neutron stars, from the surface to the inner core.

Physicists at Goethe-Universität have now developed more than a million different equations of state that meet the limitations imposed by data from theoretical nuclear physics on the one hand and astronomical observations on the other.


In doing so, scientists discovered that ‘light’ neutron stars (those with masses less than about 1.7 solar masses) have a soft mantle and a hard core, while ‘heavy’ neutron stars (those with masses greater than 1.7 solar masses) Solid. the basic. Mantle and soft core. Or, put simply: light neutron stars are like bonbons with a hazelnut in the center, surrounded by smooth chocolate, while heavy neutron stars are like bonbons with a soft filling and a crunchy crust.

The decisive factor in this vision was the speed of sound, which is the subject of undergraduate student Sinan Altibermak’s research. This quantity describes how quickly sound waves propagate in an object and depends on how hard or loose the material is. Here on Earth, for example, the speed of sound is used to explore the interior of our planet and locate oil deposits.

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Using equations of state, physicists have also been able to reveal other unexplained properties of neutron stars. Thus, regardless of its mass, it would likely only have a radius of eight miles.

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