Enlarge / The two newly captured galaxies, with the older one on the right.
One of the design goals of the James Webb Space Telescope was to provide imaging capability at wavelengths that would reveal the first stars and galaxies in the Universe. Now, just weeks after its first images were revealed, we have a strong indication that it is a success. In some of the data that NASA has made public, researchers have detected up to five galaxies in the distant Universe, already present only a few hundred million years after the Big Bang. If confirmed to be as distant as they appear, one of them will be the most distant galaxy observed to date.
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For many of its observatories, NASA allows astronomers to submit observation proposals and allows those users to have exclusive access to the resulting data for a later time. 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 them include locations similar to one of the first published images, where a large foreground galaxy cluster acts as a lens to magnify more distant objects.
(You can see details of one of the data sets used for this analysis, called GLASS, which used the Abell 2744 cluster to magnify distant objects, which were further magnified by the telescope.)
The images in this data set were long exposures taken in different parts of the infrared spectrum. The full wavelength range covered by the NIRCam instrument was divided into seven slices, and each slice was imaged for 1.5 to 6.6 hours. A large international team of researchers used these pieces 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 missing in others.
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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 formation of the cosmic microwave background. These would absorb any light at or above a wavelength sufficient to ionize hydrogen, essentially making the Universe opaque at those wavelengths. At the time, that cut was somewhere on the UV end of the spectrum. But in the intervening time, the expansion of the Universe shifted this cutoff to the infrared part of the spectrum, one of the key reasons why the Webb was designed to be sensitive to these wavelengths.
First you don’t see it (left), then you do. Inverted brightness images show an object appearing in a region of space highlighted by crosshairs, but only at longer wavelengths.
So the team looked for objects that were present in the images of the lower-energy fragments of the infrared spectrum captured by Webb but absent from the higher-energy fragments. And the precise point at which it disappeared indicates the redshift of the cutoff for that galaxy, and thus how far away the galaxy is. (You can expect future research to include a similar approach.)
This method produced five different objects of interest, and a draft manuscript focuses on the two most distant of these: GLASS-z13 and GLASS-z11. The former is even farther than the farthest confirmed distance of anything detected in Hubble’s deep field; if confirmed, this would make it the most distant object we know of, and thus the closest in time to the Big Bang.