Improved Spin and Density Correlation Simulations Give Researchers Clearer Insights on Neutron Stars

The Science

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 has calculated spin and density correlations in neutron matter using 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 researchers used computational techniques to simulate neutron matter. They also developed a new algorithm that greatly reduces the computational effort needed to calculate key information on simulations involving multiple particles.

The Impact

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. This work calculates how spin and density distributions affect the neutrino-induced heating of neutron-rich matter. It provides important data for calibrating codes used in supernova simulations.

Summary

A team of researchers from the United States, China, Turkey, and Germany performed ab initio (from the most fundamental principles) simulations to compute spin and density correlations in neutron matter using realistic nuclear interactions. The team performed the new calculations at higher neutron densities than had previously been explored. The results can be used to calibrate codes used for realistic simulations of core-collapse supernova.

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.

Funding

This work was supported by the Guangdong Major Project of Basic and Applied Basic Research, the National Natural Science Foundation of China , China Postdoctoral Science Foundation. Individual researchers were supported by the U.S. National Science Foundation, the Department of Energy Office of Science, Nuclear Physics program, the NSAF, the European Research Council, Deutsche Forschungsgemeinschaft, and the Chinese Academy of Sciences. Computational resources were provided by the Oak Ridge Leadership Computing Facility at Oak Ridge National Laboratory, the Southern Nuclear Science Computing Center in the South China Normal University, the Gauss Centre for Supercomputing at the Jülich Supercomputing Centre (JSC), and the Institute for Cyber-Enabled Research at Michigan State University.