A huge explosion from a hitherto unidentified source, which is 10 times more vigorous compared to a supernova — could be the solution to a 13-billion-year-old Milky Way mystery.
Astronomers headed by David Yong, Gary Da Costa and Chiaki Kobayashi from Australia’s ARC Centre of Excellence in All Sky Astrophysics in 3 Dimensions (ASTRO 3D) at the Australian National University (ANU) have possibly found proof of the disintegration of a collapsed swiftly spinning star — a phenomenon known as a “magneto-rotational hypernova” by the researchers.
This cataclysm, which was hitherto unknown, took place a billion years following the Big Bang and is the most probable explanation for the existence of remarkably high amounts of few elements detected in another extremely ancient and “primitive” Milky Way star.
Named SMSS J200322.54-114203.3, the star comprises greater amounts of metal elements, such as europium, uranium, zinc and possibly gold, compared to others of the same age.
Neutron star mergers which are the accepted sources of the material required to form them are not sufficient to describe their existence.
The astronomers evaluated that only the severe collapse of a very early start, which was amplified by quick rotation and the existence of a strong magnetic field, can explain the extra neutrons needed. The study was recently reported in the Nature journal.
The star we’re looking at has an iron-to-hydrogen ratio about 3000 times lower than the Sun—which means it is a very rare: what we call an extremely metal-poor star. However, the fact that it contains much larger than expected amounts of some heavier elements means that it is even rarer—a real needle in a haystack.
David Yong, ARC Centre of Excellence in All Sky Astrophysics in 3 Dimensions, Australian National University
In the universe, the first stars were composed entirely of helium and hydrogen. They broke down and exploded over several years, thus becoming black holes or neutron stars, generating bulkier elements that became embedded, in small amounts, into the next generation of stars — the oldest stars that are still present.
In recent times, the rates and energies of such star deaths have become familiar, so the amount of bulky elements they generate is well evaluated. Moreover, in the case of SMSS J200322.54-114203.3, the totals do not just get added up.
The extra amounts of these elements had to come from somewhere. We now find the observational evidence for the first time directly indicating that there was a different kind of hypernova producing all stable elements in the periodic table at once — a core-collapse explosion of a fast-spinning strongly-magnetized massive star. It is the only thing that explains the results.
Chiaki Kobayashi, Associate Professor, University of Hertfordshire
Right from the late 1990s, hypernovae have been known. Yet, this is the first time one has been detected with both quick rotation and powerful magnetism.
According to Dr. Yong, “It’s an explosive death for the star. We calculate that 13 billion-years ago J200322.54-114203.3 formed out of a chemical soup that contained the remains of this type of hypernova. No one’s ever found this phenomenon before.”
J200322.54-114203.3 is located about 7500 light-years from the Sun and orbits in the halo of the Milky Way.
Nobel Laureate Professor Brian Schmidt, who is another co-author of the study and ANU Vice-Chancellor, noted that “The high zinc abundance is a definite marker of a hypernova, a very energetic supernova.”
Professor Gary Da Costa from ANU, who is the head of the First Stars team in ASTRO 3D, described that the star was initially spotted by a project known as the SkyMapper survey of the southern sky.
“The star was first identified as extremely metal-poor using SkyMapper and the ANU 2.3m telescope at Siding Spring Observatory in western NSW. Detailed observations were then obtained with the European Southern Observatory 8m Very Large Telescope in Chile,” added Da Costa.
This is an extremely important discovery that reveals a new pathway for the formation of heavy elements in the infant universe.
Lisa Kewley, Professor and Director, ARC Centre of Excellence for all Sky Astrophysics in 3D
The other members of the research group are based at the Massachusetts Institute of Technology in the United States, Stockholm University in Sweden, the Max Planck Institute for Astrophysics in Germany, Istituto Nazionale di Astrofisica in Italy and the University of New South Wales in Australia.
Yong, D., et al. (2021) r-Process elements from magnetorotational hypernovae. Nature. doi.org/10.1038/s41586-021-03611-2.