NASA’s new toy may have already spotted the oldest known galaxy

Enlarge / The two newly imaged galaxies, with the oldest on the right.

One of the design goals of the James Webb Space Telescope was to provide the ability to image at wavelengths that would reveal the first stars and galaxies in the Universe. Now, just weeks after its first footage was revealed, we’re getting a strong indication that it’s a hit. In some of the data made public by NASA, researchers have spotted up to five galaxies in the distant Universe, already present just a few hundred million years after the Big Bang. If confirmed to be as distant as they seem, one of them will be the most distant galaxy ever observed.


For many of its observatories, NASA allows astronomers to submit observation proposals and allows those users exclusive access to the resulting data for a period of time thereafter. But for its newest instrument, NASA has a set of goals where the data will be made public immediately, for anyone to analyze as they wish. Some of these include locations similar to one of the earliest published images, where a large galaxy cluster in the foreground acts as a lens to magnify more distant objects.

(You can check out the details of one of the datasets used for this analysis, called GLASS, which used the Abell 2744 cluster to magnify distant objects, which were then magnified by the telescope.)

The images in this dataset were long exposures taken at different bits of the infrared spectrum. The full range of wavelengths covered by the NIRCam instrument was split into seven chunks, and each chunk was imaged for 1.5 to 6.6 hours. A large international team of researchers used these chunks to perform an analysis that would help them identify distant galaxies by looking for objects that were present in some parts of the spectrum but absent from others.

The research was based on the understanding that most of the Universe was filled with hydrogen atoms for hundreds of millions of years after the cosmic microwave background formed. These would absorb any light at or above a wavelength sufficient to ionize hydrogen, essentially rendering the Universe opaque at those wavelengths. At the time, this cutoff was somewhere in the UV end of the spectrum. But in the meantime, the expansion of the Universe has moved this cutoff into the infrared part of the spectrum, one of the main reasons the Webb was designed to be sensitive to these wavelengths.

First you don't see it (left), then you see it.  Brightness-inverted images show an object appearing in a region of space highlighted by crosshairs, but only at longer wavelengths.

First you don’t see it (left), then you see it. Brightness-inverted images show an object appearing in a region of space highlighted by crosshairs, but only at longer wavelengths.

The team therefore looked for objects present in images of the lowest energy chunks of the infrared spectrum imaged by Webb but absent from the higher energy chunks. And the precise point at which it disappeared indicates how redshifted the cutoff is for that galaxy, and therefore how far away the galaxy is. (You can expect future research to involve a similar approach.)

This method has produced five different objects of interest, and a draft manuscript focuses on the two most distant of them: GLASS-z13 and GLASS-z11. The former is even further than the furthest confirmed distance of anything spotted in the Hubble Deep Field; if confirmed, this would make it the most distant object known to us and therefore the closest in time to the Big Bang.

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