JWST's keen infrared eyes can deliver observations of the furthest galaxies known. This is one of the goals of the telescope: to see further back into the past than any other instrument before. It appears that it is doing that very well. A few papers shared on the research repository ArXiV show that even from the first scientific data, there are dozens of galaxies from the first few hundred million years of the universe.
Different teams found many extremely distant galaxies. Last week, the candidate for most distant objects were galaxies whose light came from about 320 million years after the Big Bang. Now, a new paper suggests that “Maisie’s Galaxy” could be the furthest, with light coming from when the Universe was just 300 million years old. This was measured as part of the CEERS collaboration.
However, this record is challenged not by a single other galaxy, but by tens of others. Another paper, submitted to Nature and awaiting peer review, looked at the galaxies in the SMACS 0723 image reports of 88 candidate galaxies whose light came to us from between 420 million and 180 million years after the Big Bang.
The distance of galaxies is estimated by measuring their redshift. Due to the expansion of the Universe, almost every galaxy that we can see appears like it is moving away from the Milky Way. This effect causes its light to shift slightly to lower (redder) wavelengths. This is similar to the siren of an ambulance moving away from you; as that happens, the siren’s pitch gets lower.
Redshift can be measured precisely by studying the spectrum of light of a galaxy. The chemical fingerprints of the elements have very precise wavelengths, so by working out their shift, one can estimate the correct redshift. This is known as spectroscopic redshift and it’s quite laborious. A faster way is to estimate the photometric redshift, which has much larger uncertainties, unfortunately.
All these distance estimates are from photometric redshift, so while exciting they will need to be confirmed with spectroscopic measurements – the good thing is that JWST has the capabilities to do just that. While maybe none of these galaxies are quite as far away as they look, the studies go to show just the extraordinary capabilities of this new space observatory.