Advanced 3D computer simulations closely mirror actual light observations neutron star fusions, enhancing our understanding of the origins of heavy elements.
An advanced new three-dimensional (3D) computer simulation of the light emitted after the merger of two neutron stars produced a similar sequence of spectroscopic features to the observed kilonova. “The unprecedented agreement between our simulations and the observation of kilonova AT2017gfo shows that we have a broad understanding of what happened during the explosion and its aftermath,” said GSI/FAIR scientist Luke J. Shingles and lead author of the publication. It Astrophysical Journal Letters. Recent observations that combine both gravitational waves and visible light point to merging neutron stars as the primary production site for this element.
The mechanics behind radiative transfer simulations
Interactions of electrons, ions, and photons within the material ejected by neutron-star mergers determine the light we can see through telescopes. These processes and the emitted light can be modeled by computer simulations of radiative transfer. Recently, researchers created for the first time a three-dimensional simulation that itself tracks the merger of neutron stars, neutron nucleosynthesis, energy stored in radioactive decay, and tens of millions of atomic transitions of heavy elements. .
Being a 3D model, the observed light can be projected from any viewing direction. When viewed nearly perpendicular to the plane of the orbits of the two neutron stars (as observational evidence suggests for the kilonova AT2017gfo), the model predicts a sequence of spectral distributions very similar to that observed for AT2017gfo. Research in this area will help us understand the origin of elements heavier than iron (such as platinum and gold), which are mostly produced by the rapid capture of neutrons during neutron star mergers, Shingles said.
Kilonova. eruption and aftermath
About half of the elements heavier than iron are produced in an environment of extreme temperatures and neutron density, which is achieved when two neutron stars merge together. When they eventually spiral into each other and merge, the resulting explosion causes matter to be ejected under the right conditions to produce neutron-rich heavy nuclei in a sequence of neutron captures and beta-decays. These cores decay to stability, liberating energy that powers an explosive kilonova transient, a bright emission of light that quickly fades in about a week.
3D simulations combine several areas of physics, including the behavior of matter at high densities, the properties of unstable heavy nuclei, and atom– light interaction of heavy elements. Other challenges remain, such as accounting for the rate of change of the spectral distribution and describing the emission at late times.
Future progress in this area will increase the precision with which we can predict and understand features in the spectrum, and will advance our understanding of the conditions under which heavy elements are synthesized. A key component of these models is the high-quality atomic and nuclear experimental data that will be provided by the FAIR facility.
Reference. Self-consistent 3D beam transfer for Kilonovae. directional spectra from merger simulations Luke J. Shingles, Christine E. Collins, Vimal Vijayan, Andreas Flers, Oliver Just, Gerrit Leck, Xavi Xiong, Andreas Bauswein, Gabriel Martnes, and P. Stewart A. Sim, September 8, 2023 The Astrophysical Journal Letters.
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