Research Byte
Published in the RSAA Lunations
Vol1 Issue17 1–30 June 2021
How were the heaviest elements in the Periodic Table produced in the early universe? In 2016-2017, neutron star mergers were confirmed as an astrophysical site for producing the rapid neutron-capture process (r-process) elements such as gold and silver. However, when including neutron star mergers alone, numerical simulations cannot explain the amount of r-process elements in the universe, particularly at the lowest abundances. Another astrophysical site is required, but what is it?
To answer that question, we need to study the chemical abundance patterns of large numbers of ancient, metal-poor, stars. With such a sample, we can discover individual objects with “chemical fingerprints” (i.e., nucleosynthetic signatures) that reveal another stellar source of the r-process elements. But first we need that large sample of ancient stars.
Since 2014, the SkyMapper telescope has been imaging the southern sky with a special set of filters designed to identify chemically primitive stars. Thanks to heroic efforts by Mike Bessell and others at RSAA, thousands of ancient metal-poor stars have been observed with the ANU 2.3m telescope. The 150 most promising candidates were observed with the Keck, Magellan and ESO telescopes to study their chemical compositions.
One object, SMSS 2003-1142, displayed a unique chemical signature; large enhancements in the abundances of nitrogen, zinc and r-process elements. Among the most chemically ancient stars, SMSS 2003-1142 has the largest enhancement of the r-process elements. The chemical abundance pattern we observe in SMSS 2003-1142 was produced by a previous star that was: (i) rapidly rotating (to produce nitrogen), (ii) exploded as an extremely energetic supernova (to produce zinc) and (iii) ejected neutron-rich material. Such an object is known as a magnetorotational hypernova. Therefore, SMSS 2003-1142 provides evidence for a new type of cosmic explosion, magnetorotational hypernovae, that can produce r-process elements like gold and silver in the early universe.
David Yong & Gary Da Costa on behalf of the team.
