Visualizations of Simulations

The origin of the heavy elements in our universe is an open problem in astronomy. The production of the heavy element is formed through a certain type of nucleosynthesis called rapid neutron capture process or r-process. The environment required for r-process requires a neutron rich environment and for many years it was thought that the only production sites could be from supernova explosions. However, more detailed numerical simulations have shown that the environments from supernovas isn’t neutron-rich enough and that another source is required. New simulations from binary neutron star (BNS) mergers have been very promising candidates for the progenitors of the heavy elements.

In order to study r-process nucleosynthesis, the history of the fluid element is required, along with key properties that are illustrated in the animation. These include density, electron fraction, and kinetic energy. By taking the time series of this data and plugging it into a nuclear network, abundancy curves of heavy elements can be produced.

In this animation, we show the merger of two 1.35 solar mass neutron stars with the LS220 equation of state. To capture the evolution of the fluid, we use tracers that can track the evolution of the fluid elements through time. The distribution of the tracers can provide insight into how the heavy elements are made.

The code used is the EinsteinToolkit with WhiskyTHC.


The original high quality version of the video can be found here.


 

The following movie shows the density evolution of the same simulation in full 3D. The color map has a logarithmic scale and thus captures the dense neutron star matter as well as the outflowing material.

In this case the formation of a bar shaped hyper massive neutron star (HMNS), which emits intense gravitational waves, is clearly visible. After loosing enough angular momentum, the HMNS collapses to a Kerr black hole surrounded by an accretion disk.


The original high quality version of the video can be found here.


 

The simulations above model BNS systems in a quasi-circular configuration. Primordial BNS systems should be found in these kind of orbits, due to the long-term emission of gravitational waves, which efficiently circularize the initial, probably eccentric orbit.

Another possibility is a BNS merger due to dynamical encounters in highly dense stellar systems, like core-collapsed stellar clusters. These events potentially release more unbound material to their surroundings, while having lower event rates.

This animation shows an eccentric encounter of two 1.39 solar mass neutron stars. They move on a parabolic orbit with a periastron of approximately 18 km. During the first encounter the strong tidal interactions lead to a large amount of neutron rich outflows and part of the orbital angular momentum is transferred to spin of the stars.

Again a LS220 equation of state is employed. In addition to the density, the internal energy and the electron fraction of the material is shown.


The original high quality version of the video can be found here.