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Finger prints of heavy elements in neutron star collisions


Do some of the heaviest elements in our universe come from the collision of neutron stars? The answer may be gained from how the luminosity of such an event evolves over several weeks. A group of scientists from GSI and FAIR, TU Darmstadt, the National Academy of Sciences of Taiwan and Columbia University, USA, recently published the respective results in the journal Physical Review Letters.

The first observation of a neutron star collision in 2017, which was detected by gravitational wave detectors, caused a sensation also in the field of nuclear physics. As predicted by GSI scientists, there were clear indications that heavy atomic nuclei would be produced in these extreme cosmic events. But exactly which nuclei are produced in neutron star collisions is still unclear.

"The luminosity of the neutron star collision reveals which elements are formed during this event," says GSI scientist Professor Gabriel Martínez-Pinedo, who contributed substantially to this publication and also was involved in the predictions on nuclei synthesis in neutron star collisions. "At the event in 2017 we couldn’t observe this as the neutron star collision disappeared behind the sun. That’s why we couldn’t fully observe the light emissions at a crucial stage.” But the next observations of neutron star collisions are expected soon. In order to be able to analyze them, Martínez-Pinedo and his colleagues have made predictions about how the luminosity of the neutron star collision will evolve, depending on which nuclear-physical processes take place during the fusion and which heavy elements are produced.

About one month after the event, there are only about 30 different nuclei left to influence the luminosity, because nuclei with short lifetimes already decayed. Some heavy isotopes dominate the energy output and thus influence the intensity and duration of luminosity, for example Californium-254, followed by Radium-223, Actinium, and lastly, Radium-225. “When telescopes record the next neutron star collision in high resolution, thanks to our model we can probably conclude from the luminosity changes over weeks which heavy elements have been formed and how the nuclear synthesis process unfolds," says Martínez-Pinedo.

The models that are used to predict luminosity and duration contain many nuclear properties that are not yet fully understood. This is where research at the FAIR accelerator facility, which is currently under construction, comes into play. The experiments of the FAIR collaboration NUSTAR are mainly aimed at generating and investigating the heavy nuclei produced by neutron star collisions or supernovae. At FAIR, this can be done in the laboratory with the help of particle accelerators. "With FAIR, we will be able to explore the universe in the laboratory," says Professor Karlheinz Langanke, Research Director of GSI and FAIR. "FAIR will be a unique facility worldwide, allowing researchers to bring the diversity of the universe into the lab to investigate fundamental questions such as the origin of chemical elements in the universe.” (LW)

More information

Original publication: Fingerprints of Heavy-Element Nucleosynthesis in the Late-Time Lightcurves of Kilonovae

The first image of a neutron star collision recorded by Hubble Space Telescope.
Image: NASA and ESA. Acknowledgment: N. Tanvir (U. Leicester), A. Levan (U. Warwick), and A. Fruchter and O. Fox (STScI)