An Ancient Hypernova Filled This Star With Unusual Elements

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An Ancient Hypernova Filled This Star With Unusual Elements
The star SMSS J200322.54-114203.3 at center, imaged as part of the SkyMapper survey.
The star SMSS J200322.54-114203.3 at center, imaged as part of the SkyMapper survey.
Image: Da Costa/SkyMapper

The peculiar elemental makeup of one star in the Milky Way could be due to a massive type of stellar collapse in the early universe, a team of astronomers announced today. The finding could help astronomers understand the diversity of ways in which the universe’s heavy elements, like gold, originated.

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The star in question, SMSS J200322.54-114203.3, is 7,500 light-years from the Sun and sits in the halo on the periphery of our galaxy. The team believes a stellar explosion even more energetic than a supernova—called a “hypernova”—is responsible for the star’s unusual chemistry. Elements heavier than iron require intense forces to be created: The merging of neutron stars, as well as the collapse of large stars in supernova explosions, are two common ways. Heavy elements are forged when lighter elements absorb many neutrons, some of which decay into protons, eventually landing on a stable isotope of a heavy element. Those elements are then dispersed into the interstellar medium by the force of the explosion or collision, eventually ending up in other stars and on planets like Earth.

Scientists say this particular star’s chemistry—a very low iron content and very high amounts of nitrogen, zinc, europium, and thorium—pointed to a different source of heavy elements than the typical neutron star merger. Their research is published today in Nature.

“The key question this research addresses is, ‘How were the heaviest elements produced in the early universe?’” said David Yong, an astronomer at the Australian National University and lead author of the recent paper, in an email. “The mergers of neutron stars (the extremely dense remnants of massive stars) were recently confirmed as sources … Our results reveal magnetorotational hypernova (an energetic explosion of a rapidly rotating star with magnetic fields) as another source of those heavy elements.”