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Early Universe

An exciting era of exploration

Nature Astronomy volume 7, pages 514–515 (2023)Cite this article

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Long-exposure spectra taken with the James Webb Space Telescope (JWST) reveal the most distant galaxies ever observed — back to a time when the Universe was only 2% of its present age.

Largely owing to several expertly designed programmes with open data access3,4 the first six months of JWST science operations have been truly extraordinary, and these are not the first, or even the most distant, JWST-discovered galaxies that have been announced. As an example, two bright galaxies with possible redshifts of z = 16–17 have been described5,6. The operative word here is ‘possible’: the vast majority of very distant galaxies come with the warning label: ‘unless shown to be something else’. The gold standard for redshift measurements is the identification of one or more distinct lines or features in a spectrum, as this provides a measurement that is both unambiguous and precise. However, it is far less costly (in terms of telescope time) to obtain images than spectra, and since the 1990s distant galaxies have been successfully and ubiquitously identified by their multi-band colours, measured from images, rather than specific features measured from spectra7. This is fine when the methods and uncertainties are well-understood but dangerous when working at a new frontier — as we are now doing with JWST.

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Fig. 1: Two instruments working in tandem.

NASA, ESA, CSA, M. Zamani (ESA/Webb), Leah Hustak (STScI)

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  1. Astronomy Department, Yale University, New Haven, CT, USA

    Pieter van Dokkum

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  1. Pieter van Dokkum
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Correspondence to Pieter van Dokkum.

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van Dokkum, P. An exciting era of exploration. Nat Astron 7, 514–515 (2023). https://doi.org/10.1038/s41550-023-01946-6

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