When the James Webb Space Telescope (JWST) project released its first full-colour images last week, in among the stunning starscapes was a that has nonetheless set astronomers’ hearts aflutter. The diagram shows the fingerprint-like spectrum of light from an inconspicuous red background galaxy (pictured above) in the telescope’s “deep field” image, and its undulating peaks and troughs represent an unprecedented insight into a galaxy living in the early universe.
The spectrum itself was produced by JWST’s NIRSpec instrument, which uses tiny windows to isolate and analyse the light from objects within the field of view of the telescope. In this case, only the ancient galaxy’s starlight was allowed to pass through in order to reveal its chemical signatures.
Such had been the secrecy around the capture and release of the first JWST observations that some of the NIRSpec team weren’t even aware of the existence of the spectrum until the public announcement on 12 July. But there was one feature of the data that NIRSpec team member , at the University of Oxford, saw was “a real step [forward] within minutes of the data being released”.
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Among the various hallmarks of different elements within the galaxy was a particular fingerprint – what astronomers call an emission line – of glowing oxygen gas, with a wavelength of 436.3 nanometres. The NIRSpec team had hoped to observe this emission line in extremely distant galaxies, says Bunker, but anticipated having to search “dozens or hundreds” of targets to uncover it. “I don’t think we really dreamt that within the first, essentially publicity, snap that it would be there. That’s really quite incredible,” he says. It is all so sudden that the galaxy doesn’t even appear to have a name.
The oxygen line is so important because astronomers use it to calibrate their measurements of the compositions of galaxies. If you can see this line with your instruments, and are able to compare it to other oxygen emission lines in a galaxy’s light, you unlock a way to translate the apparent prominence of different chemical fingerprints in a spectrum to how much of those chemicals are really in the galaxy. żěè¶ĚĘÓƵs had done this for nearby galaxies before, says Bunker, but not for far-off ones like the smudge of light scrutinised in the new data.
Future JWST spectra, like this early example, will allow researchers to explore how the proportion of elements heavier than helium in distant galaxies has changed over time. “It gives you data points on that evolution,” says , an astrophysicist at the University of Nottingham, UK. “So you can start to think how quick did the first stars die and pollute the gas [to] create the second generation of stars of which this galaxy is made.”
Insights like these have the potential to revolutionise what we know about the early universe. “There is a missing billion years in our understanding of the evolution of our universe,” says Chapman. “From around 380,000 years after the big bang to about a billion years after we have very little information. Now JWST is being able to dive right back into that era.”
Soon the telescope will be examining even more distant galaxies, capturing more spectra along the way. Bunker says it is even likely that JWST will, imminently, break the record for the most distant galaxy ever observed. “I’m pretty sure that that will be delivered on, perhaps not tomorrow but certainly within months,” he says.
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