Window on the Universe: Equation of State of Asymmetric Nuclear Matter

Michigan State University, East Lansing MI

Investigators

Abstract

Windows on the Universe: Equation of state of Asymmetric Nuclear Matter The spectacular GW170817 gravitational wave (GW) observations of a Neutron Star (NS) merger by the LIGO-Virgo collaboration were accompanied by the detection of gamma-rays, optical and radio signals. These coordinated observations were the fruit of cutting-edge scientific investments by the U.S. These investments usher in a new era of synchronous multi-messenger astrophysics, and provide definitive links between NS mergers, kilonovae and gamma-ray bursts, and between NS mergers and the nucleosynthesis of heavy elements. The proposed research plan broadens these multi-messenger studies to include relevant messages from experimental constraints on the forces within neutron-rich matter that support the NS. It addresses questions of the 2015 Long Range Plan for Nuclear Science concerning the nature of neutron stars and dilute and dense nuclear matter by focusing on properties of nuclear forces that depend on neutron-to-proton imbalance. Michigan State University and FRIB sponsor research for under-represented physics students, which will help to attract a diverse group of talented undergraduate students, graduate students and postdocs to this project. These young scientists will learn about detector design and construction, complex multi-parameter data analyses, detector simulations and theoretical modeling, machine learning and Bayesian inference analyses. This training prepares them for leadership roles in the future work force both in nuclear science but also in other key areas important for technological advancement and national security. Both the GW170817 gravitational wave observations and recent messages on Neutron Star (NS) radii from the Neutron star Interior Composition Explorer (NICER) constrain the relationship between the total pressure and the matter density within NS. Neither astronomical observation isolates the symmetry energy, however. The symmetry energy is a term in the Equation of State (EoS) that arises from the imbalance in the numbers of neutrons and protons in the matter. It plays a dominant role regarding the stability of a NS. The symmetry energy governs the relative numbers of neutrons and protons, and the density and pressure where the liquid NS core ends and solid crust begins. The symmetry energy also governs whether anti matter or strange matter exist within neutron stars. The group will study the symmetry energy via experimental studies and isolate its role by varying the relative numbers of neutrons and protons and also the density of the system from ¼ to twice normal nuclear matter density. They will perform experiments at RIKEN in Japan, using cutting edge instrumentation and a collaborative effort between theory and experiment to connect the findings to emerging results from multi-messenger astronomy. By combining these new measurements of the symmetry energy with existing experimental constraints on the EoS of symmetric matter which contains equal numbers of neutrons and protons, they will also obtain the EoS of pure neutron matter which is also of fundamental interest. While the focus of the student training is on scientific and technological advancement, they will also engage young scientists in outreach activities to make this science more accessible to non-scientists. They have created websites using virtual reality apps to illustrate nuclear collisions, the detection of cosmic rays and the working principles of our time projection chamber. By such efforts, they will endeavor to make the science more appealing and exciting to the general public. This project advances the objectives of "Windows on the Universe: the Era of Multi-Messenger Astrophysics", one of the 10 Big Ideas for Future NSF Investments. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.