Nucleosynthesis and observation of the heaviest elements

Abstract

The rapid neutron capture or ‘r process’ of nucleosynthesis is believed to be responsible for the production of approximately half the natural abundance of heavy elements found on the periodic table above iron (with proton number $$Z=26$$ Z = 26 ) and all of the heavy elements above bismuth ($$Z=83$$ Z = 83 ). In the course of creating the actinides and potentially superheavies, the r process must necessarily synthesize superheavy nuclei (those with extreme proton numbers, neutron numbers or both) far from isotopes accessible in the laboratory. Many questions about this process remain unanswered, such as ‘where in nature may this process occur?’ and ‘what are the heaviest species created by this process?’ In this review, we survey at a high level the nuclear properties relevant for the heaviest elements thought to be created in the r process. We provide a synopsis of the production and destruction mechanisms of these heavy species, in particular the actinides and superheavies, and discuss these heavy elements in relation to the astrophysical r process. We review the observational evidence of actinides found in the Solar system and in metal-poor stars and comment on the prospective of observing heavy-element production in explosive astrophysical events. Finally, we discuss the possibility that future observations and laboratory experiments will provide new information in understanding the production of the heaviest elements.

Spectacular Nucleosynthesis from Early Massive Stars

“…Our star J0931 + 0038 has a full complement of first neutron-capture peak elements from Sr to Pd and nothing beyond, which makes it most similar to HE 1327−2326ʼs much sparser abundance pattern. Note that the pattern is flat in [X/Fe], which differs substantially from the "pure" r-process pattern in SMSS J2003 −1142, as well as theoretical r-process predictions (Holmbeck et al 2023).…”

“…The elements from Sr and heavier are formed primarily through the slow (s) and rapid (r) neutron-capture processes, though proton-capture and i-processes are possible as well. In J0931 + 0038, the very low [Ba/Fe] rules out a strong, neutron-rich r-process (e.g., from neutron star mergers; Holmbeck et al 2023) and the main sprocess (e.g., Lugaro et al 2012). Most remaining scenarios to explain the high [Sr-Pd/Fe] invoke nucleosynthesis associated with the formation of neutron stars or black holes, with the i-process activated in external Herich layers as an alternative.…”

Superheavy Elements in Kilonovae

“…In this study, we have explored and selected a combination of nuclear data and astrophysical conditions that allows production of superheavy elements in order to examine their potential impact on observables (i.e., kilonova light curves). So far, no evidence of the natural production of Z 104 elements has been definitively found (though see claims of superheavy decay products found in meteorites; references in Holmbeck et al 2023). If superheavy elements have a unique effect on light curves, it may be possible to infer their production in NSMs.…”

“…An earlier signal could possibly arise from the energetic decay of even heavier nuclei: the "superheavy" elements with Z 104. Whether these elements are even produced by nature is a topic of debate and depends sensitively on the nuclear physics at high proton and neutron numbers (Holmbeck et al 2023). In this work, we explore a subset of nuclear models that Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence.…”

Nuclear Reactions in Evolving Stars (and Their Theoretical Prediction)

“…For applications to astrophysical question see e.g. (Martinez-Pinedo et al, 2007;Petermann et al, 2012;Erler et al, 2012;Eichler et al, 2015;Giuliani et al, 2018;Eichler et al, 2019;Giuliani et al, 2020;Kullmann et al, 2023;Holmbeck et al, 2023).…”