Life’s ingredients found in the ashes of an exploded star

Astronomers used Japan’s XRISM spacecraft to detect clear X-ray signatures of chlorine and potassium in the debris of a well-known supernova. Potassium appears in the data with extremely high confidence, exceeding the 6-sigma level.

The signals come from Cassiopeia A (Cas A), a supernova remnant, the expanding debris of a dead star inside our Milky Way. 

A new study reports that these rare elements appear in far higher amounts than standard calculations predicted.

Stars that seed life on Earth

The work was led by Toshiki Sato, an astrophysicist at Meiji University in Tokyo. His research focuses on high resolution X-ray spectroscopy of supernova remnants and the physics of stellar explosions.

According to a report from NASA, the team connected the stellar deaths to the ingredients of life on Earth.

“This discovery helps illustrate how the deaths of stars and life on Earth are fundamentally linked,” said Sato.

These lines were measured in the southeast and northern parts of the remnant, where the debris is richest in oxygen and silicon.

The observed pattern points to turbulent interiors shaping what a star makes before it dies.

Why odd elements matter

Chlorine and potassium are odd-Z elements, elements with odd proton counts.

These elements are practical and familiar. Chlorine helps form salts, while potassium supports nerve signals and the activity of heart muscle.

Stars usually forge even-numbered elements more easily, which is why odd ones tend to be scarce.

Cas A, however, breaks that rule, displaying ratios close to solar values – roughly 1.3 for potassium relative to argon, and about 1.0 for chlorine relative to sulfur.

Odd-numbered elements form through fragile balances of neutron and proton captures that shift with temperature and mixing. That sensitivity makes them valuable tracers of a star’s otherwise hidden interior.

Clear supernova signals

XRISM’s Resolve spectrometer uses a microcalorimeter, a sensor that measures tiny heat changes to read the energy of incoming X-ray photons. It reaches about 5 eV resolution near 6 keV.

Earlier detectors blurred nearby lines into a single lump for decades. Resolve slices those lines cleanly, so faint signals from rare elements are no longer buried.

The instrument is compact but razor-precise, built around a 36-pixel array engineered for accuracy.

By design, it sacrifices wide coverage in favor of the clarity needed to tackle the hardest spectral problems.

A star that shed life’s ingredients

The abundance pattern suggests strong mixing inside the star before it exploded. Likely culprits include fast rotation, binary interactions, or a short-lived shell merger that churned the burning layers.

Cas A itself is a type IIb event, a classification based on a recovered spectrum of the original blast. This type typically points to a star that shed most of its hydrogen envelope, often with help from a companion.

The potassium line is strongest where oxygen rich clumps lie, which fits a pre-explosion origin. The western region shows only weak hints, reinforcing the picture of an asymmetric star.

Why this changes the story

Seeing chlorine and potassium where theory did not expect them forces a rethink of how stars prepare the periodic table. These are not exotic curiosities – they are ingredients used by planets and living cells here on Earth.

The detection also shows what precision X-ray spectroscopy, measuring how matter emits light by energy can reveal about hidden physics. It ties a local stellar relic to a bigger question about where our salts and nerve signals ultimately come from.

Stars carrying the ingredients of life

The team will turn XRISM to other remnants to see if Cas A is typical or a standout. If other sites show the same pattern, then internal mixing is probably a common feature of massive stars.

Modelers now have a firm benchmark for tuning their codes. The results favor scenarios that include rotation, a partner star, or temporary layer mergers deep inside the progenitor.

The map shows a lopsided distribution that aligns with earlier asymmetry hints. The chlorine and potassium enhancements sit well above standard supernova models yet agree with versions that include rotation, companion effects, or shell mixing.

Either outcome teaches something important about galaxy chemistry. A consistent pattern would rewrite our chemical evolution models, whereas a singular case would reveal a star with an exceptional history.

The study is published in the journal Nature Astronomy.

Image Credit: NASA; ESA; CSA; CXC/SAO; STScI; JPL/Caltech; Milisavljevic et al.; J. Schmidt & K. Arcand

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