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Improved spin and density correlation simulations give researchers clearer insights on neutron stars

When a star dies in a supernova, one possible outcome is for the remains to become a neutron star. Inside a neutron star, the protons and electrons combine into uncharged neutrons. This substance is called neutron matter.

A team of researchers from the United States, China, Turkey, and Germany has performed ab initio (i.e., from the most fundamental principles) simulations to calculate spin and density correlations in neutron matter. They used realistic nuclear interactions at higher densities of neutrons than previously explored. Spin and density are the probability of finding a neutron in a particular position with a particular direction of spin. These correlations determine key aspects of how neutrinos scatter and heat up in a core-collapse supernova.

The research is in the journal Â鶹ÒùÔºical Review Letters.

To perform the calculations, the researchers introduced a new algorithm called the "rank-one operator method" that greatly reduces the computational effort needed to calculate observables involving several particles. The rank-one operator method exploits a simplification in the complicated mathematics used in computing neutrino transport through dense nuclear matter, resulting in much more efficient computation. The rank-one operator method has since been applied to calculations of other observables in nuclear physics as well as other fields.

Researchers can use the results of this new study in realistic simulations of supernova explosions. Nearly all the energy released in a core-collapse supernova is carried away by neutrinos. The outward flow of neutrinos energizes the neutron-rich matter in the supernova. This increases the likelihood of an explosion.