Neutron stars seem to attract all the most delicious comparisons in astronomy. The matter inside them is believed to be organized in structures resembling "nuclear pasta" and now astronomers think that these extremely dense objects can be divided into two chocolate praline-based classes based on their masses.
Neutron stars are the end product of some supernovae when a star runs out of fuel and collapses in on itself. This collapsed core is compressed into a sphere often smaller than a city, with a radius of about 12 kilometers (7.5 miles). They are so dense just a teaspoon of neutron star weighs that of a mountain and the gravity is so intense that mountains on them are just millimeters tall. And little is known about what exactly is going on inside.
In a new paper, a team of researchers from Goethe University tried to work out a theoretical framework for the interior of neutron stars and concluded they have different internal structures depending on their mass. How are they like pralines? If they weigh more than 1.7 times our Sun, they will be heavy neutron stars and have a stiff exterior and softer core (like Lindor chocolate truffles), while lighter ones have a soft mantle and stiff core (like a Ferrero Roche).
"Neutron stars apparently behave a bit like chocolate pralines: Light stars resemble those chocolates that have a hazelnut in their center surrounded by soft chocolate, whereas heavy stars can be considered more like those chocolates where a hard layer contains a soft filling," co-author Professor Luciano Rezzolla said in a statement.
"This result is very interesting because it gives us a direct measure of how compressible the center of neutron stars can be."
They estimated the mass range for these objects, which should be between 1.4 to two times the mass of the Sun, and managed to put a constraint on how big these objects can get. The answer is not very.
"Our extensive numerical study not only allows us to make predictions for 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," Dr Christian Ecker added.
"These insights will become particularly important to pinpoint the unknown equation of state with future astronomical observations and detections of gravitational waves from merging stars."
The study is published in The Astrophysical Journal Letters.