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Astronomers in Japan say they have finally found the long-missing source of two elements essential for life.
For years, theoretical models have struggled to explain why these odd-Z elements appear in far greater quantities across the universe than stars were expected to produce.
According to a report released by Kyoto University, researchers there and at Meiji University turned to Cassiopeia A, one of the Milky Way’s best-studied supernova remnants, to search for clues. They relied on XRISM, the X-Ray Imaging and Spectroscopy Mission operated by JAXA since 2023.
The satellite’s Resolve microcalorimeter, which offers much sharper energy resolution than earlier detectors, enabled the team to pick out extremely faint emission lines linked with rare elements.
Those measurements were then compared with several established nucleosynthesis models.
Unexpected abundance
The analysis revealed that Cassiopeia A contains chlorine and potassium in quantities far exceeding predictions from standard supernova theory.
In an article from Kyoto University, the researchers explain that this is the first observational confirmation that a single exploding star can generate enough of these elements to match cosmic levels.
The researchers argue that vigorous internal mixing inside massive stars — potentially driven by rapid rotation, interactions in binary systems or shell-merger events — may boost production of these elements before the star collapses.
“When we saw the Resolve data for the first time, we detected elements I never expected to see before the launch,” said corresponding author Toshiki Sato. “Making such a discovery with a satellite we developed is a true joy as a researcher.”
Inside exploding stars
The findings suggest that substances crucial for life were forged in violent stellar environments, long before planets could form.
The team says the work also demonstrates the power of high-precision X-ray spectroscopy for investigating the invisible physics occurring deep in stars.
“I am delighted that we have been able, even if only slightly, to begin to understand what is happening inside exploding stars,” noted co-author Hiroyuki Uchida.
What comes next
Researchers aim to study additional supernova remnants with XRISM to determine whether Cassiopeia A is unique or part of a broader pattern in stellar evolution.
“How Earth and life came into existence is an eternal question,” said co-author Kai Matsunaga. “Our study reveals only a small part of that vast story.”
You can read the entire study in Nature here (opens new tab).
Sources: Kyoto University
