Three JWST sightlines put carbon and oxygen outside galaxies 500 million years after the Big Bang

Metals seen in a galaxy's own spectrum could be metals still inside the galaxy. The blueshift is how the team addressed that: the absorption sits at a velocity offset from the galaxy itself, which the authors attribute to gas moving outward and carrying heavy elements away ^[11].

The design is simple. "We used the galaxies themselves as background light sources," said Yongda Zhu, first author and a postdoctoral researcher at the University of Arizona's Department of Astronomy and Steward Observatory ^[7][18]. "As light from the galaxies traveled toward Earth, it passed through surrounding gas, and we were able to look at the light's absorption patterns to detect specific elements," he said ^[8]. Only JWST's infrared capability made the observation possible ^[17], for light that has been traveling more than 13 billion years ^[3].

Three detections make up the sample. "Hundreds" of spectra means at least two hundred examined, which puts the detections at no more than about 1.5 percent of what was inspected ^[15]. That figure measures the search. The search kept the sightlines where the absorption was strong enough for one person to notice over one night of reading public spectra ^[10].

Because each galaxy lights its own sightline, the gas doing the absorbing lies in that galaxy's surroundings ^[8]. The claim that the metals reach intergalactic space rests on the outward motion of that gas ^[11]. The report lists carbon, oxygen and silicon and gives no abundances for the three systems ^[19].

The chemistry looked mature. The fingerprints of the three closely resembled those of evolved galaxies billions of years later ^[12], at a moment about 3 percent of the universe's current age ^[2], during the Epoch of Reionization ^[4]. The expectation had run the other way: much of the gas around the first galaxies should have stayed relatively pristine, mostly hydrogen and helium ^[5]. The Arizona account of the Nature Astronomy paper says that picture is likely wrong ^[6].

Zhu's own wording keeps the seeding of neighbours conditional. "Not only were the galaxies producing these elements, but they were also dispersing them, possibly seeding other galaxies," he said ^[14]. The exchange of material between galaxies and their surroundings is called baryon cycling ^[16]. "We observed that heavy elements escaped from galaxies very, very early in cosmic time," said Zhu ^[13].