Kyoto University researchers investigating the mysterious origins of critical life-supporting elements chlorine and potassium have found compelling evidence that these rare-earth elements were produced in the extreme environment of a dying star.
Although previous studies have identified an excess of chlorine and potassium relative to predictions from stellar production models, leaving astronomers unable to explain their origin, the new data from a supernova remnant may have finally solved the longstanding mystery.
In a statement detailing the discovery, the Kyoto team and colleagues from Meiji University noted that scientists have long considered chlorine and potassium to be key ingredients in planet formation and biological life. However, the exact origins of potassium and chlorine, dubbed odd-Z elements since they contain an odd number of electrons, have remained a mystery. That’s because current stellar formation models predict that stars create roughly one-tenth of the two life-supporting elements that astronomers have observed in the universe, leaving a deficit that scientists have struggled to explain.
Curious if exploding stars that have gone supernova could account for the remaining 90%, the Kyoto University-led team studied the remnant of a Milky Way supernova called Cassiopeia A. According to the researchers, the Japanese Space Agency (JAXA) X-Ray Imaging and Spectroscopy Mission (XRISM) satellite, launched in 2023, was the ideal tool to search for the missing life-supporting elements.
After aiming XRISM’s sensitive microcalorimeter Resolve device at Cassiopeia A, the researchers collected high-resolution X-ray spectrographic data on the remnant of an exploded star. The team said this tool provided high-energy resolution of the supernova remnant, “an order of magnitude better” than previously used X-ray detectors, offering an unprecedented glimpse into the heart of a dying star.
As hoped, the instrument’s increased resolution revealed emission lines from rare earth elements that had been created in the extreme environment of the exploding star. When the team compared the spectrum data with known signatures, they found that chlorine and potassium were produced by Cassiopeia A.
Next, the team compared the results with numerous supernova nucleosynthetic models. According to the press release, this analysis revealed the telltale spectral signatures of both life-supporting elements “at abundances higher than predicted” by generally accepted supernova models.
“When we saw the Resolve data for the first time, we detected elements I never expected to see before the launch,” explained corresponding author Toshiki Sato.
The team said that discovering the presence of chlorine and potassium at such high levels offers the “first observational evidence” that exploding stars could finally explain the mysterious origins of the key ingredients for life. The Kyoto-led team also said the data suggest that ‘strong’ mixing inside massive stars, which could be caused by fast rotation, binary interaction, or shell-merger events, “can significantly enhance the production” of these life-supporting elements.
Although the study examined only a single supernova remnant, the team said their findings show that chlorine and potassium can be produced in a star’s interior in sufficient quantities to account for the previously observed deficit. The data also indicates that ingredients that are considered critical for life can be created in an extreme, intense environment “far removed from anything resembling the conditions needed for life to emerge.”
“I am delighted that we have been able, even if only slightly, to begin to understand what is happening inside exploding stars,” said corresponding author Hiroyuki Uchida.
The team said the XRISM satellite’s ability to probe the deep interiors of stars, where elements critical for life are produced, demonstrated the power of high-precision X-ray spectroscopy. When discussing the impact of the findings, Sato said that making this type of crucial discovery with a satellite his team developed “is a true joy as a researcher.”
When discussing the following steps, the team said they plan to use the high-resolution capabilities of the XRISM satellite to determine if Cassiopeia A is an exception and the mysterious origin of the excess chlorine and potassium seen throughout the universe is still an open question, or do other dying stars also create an abundance of the critical for life elements needed to make up the previously observed difference.
If future observations reveal a similar signature of chlorine and potassium at the heart of other supernovae, the team said, it will show that such internal mixing processes “are a universal feature of stellar evolution.”
In the statement’s conclusion, corresponding author Kai Matsunaga noted that where life came from is an “eternal question everyone has pondered at least once.” So, helping solve such a longstanding mystery can also provide researchers with personal value.
“Our study reveals only a small part of that vast story, but I feel truly honored to have contributed to it,” Matsunaga said.
The study “Chlorine and Potassium Enrichment in the Cassiopeia A Supernova Remnant” was published in Nature Astronomy.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.