New SONATINA 5 project awarded to Dr. Daniel Pęcak

Simulation of two atomic nuclei embedded in the "sea" of superfluid neutrons.

The project of Dr. Daniel Pęcak - SONATINA 5, financed by the National Science Center - aims to learn about the properties of the inner crust of a neutron star. Using supercomputer simulations and the latest astrophysical models, the Nuclear Theory Group will determine the interaction between nuclei immersed in a super-liquid neutron fluid. It results in macroscopic properties, for example, thermal conductivity responsible for the cooling process of neutron stars, which can be related to data from astronomical observations.

A neutron star has a layered structure, and under the surface, one can distinguish successively: the outer and outer crust and the core. In the outer crust, the atomic nuclei form a lattice similar to that found in, for example, metals on Earth, except that it is millions of times denser. The pressure resulting from strong gravity causes protons and electrons to form uncharged neutrons in the deeper layers, which account for an increasing percentage of the matter in the crust. In the inner crust, the densities are large enough, and the distances between the nuclei are so small that the neutrons begin to "leak" into the space around the nuclei. Consequently, this part of a neutron star is made up of a network made of nuclei, which interacts with the ubiquitous "fluid" of neutrons that can move freely because they are superfluid.

Next to the core border is a neutron star region characterized by the fact that the nuclei are very strongly interacting with each other and the surrounding neutrons. The interaction causes both the destabilization of the lattice and the deformation of the spherical shapes of the nuclei themselves: the new shapes include, among others, lines, planes and can even have a sponge structure. The abundance of different phases has been called nuclear noodles due to the variety of structures and shapes.

The project concerns the study of the properties of the inner crust, in particular the precise determination of interactions between the nuclei. We will shed some light on the role of interactions in both lattice deformations and the creation of the exotic phase of nuclear pasta. We will use the latest models describing the interiors of neutron stars and supercomputers with a power of 250 petaflops, that is, performing 2.5x1018 operations per second. With their help, three-dimensional simulations will be made to show how the nuclei immersed in neutron matter move, thanks to which we will find out how they interact with each other.

Project title: Influence of superfluidity in the time evolution of inhomogeneous structures in a neutron star

Project budget: 542 900 PLN