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Big Red II simulations determine the properties of nuclear pasta

Nuclear pasta: the phrase conjures images of glowing green noodles, and while it does fall into the category of a “science experiment,” it likely not what you think. Far from the consistency of cooked spaghetti, nuclear pasta is significantly more dense than ricotta gnocchi, and much harder to break than the burnt ends of a lasagna fresh from the oven. Nuclear pasta is, rather, found in the inner crust of neutron stars, and it is the strongest known substance in the universe. Researchers Matthew Caplan, a postdoctoral research fellow at McGill University and former IU graduate student, and colleagues Professor Charles Horowitz, a theoretical nuclear astrophysicist at Indiana University, and Andre Schneider, a postdoctoral researcher at Caltech, seek to understand this crust, and turned to IU’s supercomputer Big Red II in order to simulate conditions impossible to create in a lab on earth.

Example of large simulation of nuclear pasta, containing 3,276,800 protons and neutrons

When a star dies, a neutron star forms; gravity then bears down on this neutron-rich remnant at extreme pressure resulting in a substance with some strange properties. Caplan explains, “neutron stars have a very rich internal structure, with a solid crust covering a liquid core...which makes them a lot like the earth.” He and his colleagues are studying this substructure in order to better understand the properties and activity of neutron stars. Though this material is currently theoretical, Caplan and his colleagues imagine it takes the shape of tubes, and sheets, much like gnocchi, spaghetti, and lasagna, hence “nuclear pasta.” The scientists completed simulations to test the properties of nuclear pasta on IU supercomputer Big Red II, and recently published their findings in Physical Review Letters. Unlike the substance’s namesake pasta, a great deal of pressure was necessary to bend the material; the pressure required to break it, however, was greater than for any known material.

Given the density and gravity of the neutron star crust, it would be impossible to study it in a lab on earth. Thus, the scientists are, as Caplan explains, “doing the largest simulations ever of the densest material in the universe” on Big Red II. The simulations, which tested a variety of the nuclear pasta’s properties, required approximately two million hours of processor time, rendering Big Red II indispensable. Caplan reports that he would recommend Big Red II to anyone looking to do GPU supercomputing, noting that “the system is reliable and has resources, both for computing and storage” and lauding the UITS team that “works very hard to make our science possible.”