An explosion of a fast-spinning strongly magnetized star, called a magneto-rotational hypernova, is the most likely explanation for the presence of unusually high amounts of some elements detected in SMSS J200322.54-114203.3 (hereafter SMSS 2003-1142), a red giant star located 7,500 light-years away in the halo of the Milky Way Galaxy.
The red giant star SMSS J200322.54-114203.3 (center) in the south-eastern corner of the constellation of Aquila, close to the border with Capricornus and Sagittarius. Image credit: Da Costa / SkyMapper.
First identified by the SkyMapper telescope in 2018, SMSS 2003-1142 is a 13-billion-year-old extremely metal-poor star.
It contains larger amounts of metal elements, including zinc, uranium, europium and possibly gold, than other stars of the same age.
“SMSS 2003-1142 has an iron-to-hydrogen ratio about 3,000 times lower than the Sun, which means it is a very rare — what we call an extremely metal-poor star,” said Dr. David Yong, an astronomer at the ARC Centre of Excellence in All Sky Astrophysics in 3 Dimensions (ASTRO 3D) based at the Australian National University.
“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.”
Neutron star mergers — the recently confirmed sites of rapid-neutron-capture (r-process) nucleosynthesis, a process in which these elements are formed — are not enough to explain their presence.
Dr. Yong and colleagues calculated that only the violent collapse of a very early, fast-spinning, strongly magnetized star can account for the additional neutrons required.
“The extra amounts of these metal elements had to come from somewhere,” said Dr. Chiaki Kobayashi, an astronomer in the Centre for Astrophysics Research at the University of Hertfordshire and ASTRO 3D.
“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.”
Hypernovae have been known since the late 1990s. However, this is the first time one combining both rapid rotation and strong magnetism has been detected.
“We calculate that 13 billion-years ago, SMSS 2003-1142 formed out of a chemical soup that contained the remains of this type of hypernova. No one’s ever found this phenomenon before,” Dr. Yong said.
“The high zinc abundance is definite marker of a hypernova, a very energetic supernova,” added Professor Brian Schmidt, Nobel laureate and an astronomer in the Research School of Astronomy and Astrophysics at the Australian National University.
The findings were published in the journal Nature.
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D. Yong et al. 2021. r-Process elements from magnetorotational hypernovae. Nature 595, 223-226; doi: 10.1038/s41586-021-03611-2
