One of the design goals of the James Webb Space Telescope was to provide imaging capability at wavelengths that would reveal the Universe’s first stars and galaxies. Now, just a few weeks after the first images came out, we’re getting a strong indication that it was successful. In some data that NASA has made public, researchers have identified as many as five galaxies from the distant Universe already existing just a few hundred million years after the Big Bang. If confirmed to be as far away as they seem, one of them would be the most distant galaxy ever observed.
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For most of its observatories, NASA allows astronomers to submit proposals for observation, and these users have exclusive access to the data that emerges for a period of time. But for its newest tool, NASA has a set of goals where the data will be made public immediately for anyone to analyze as they please. Some of these include locations like this one of the first images releasedA large foreground cluster of galaxies acts as a lens to magnify more distant objects.
(You can view the details One of the datasets used for this analysisThe so-called CAM, which uses the Abell 2744 cluster to magnify distant objects, which are further magnified by the telescope.)
The images in this dataset were long exposures made in different parts of the infrared spectrum. All of the wavelengths covered by the NIRCam instrument were split into seven segments, and each segment was imaged for anywhere from 1.5 to 6.6 hours. A large international team of researchers used these fragments to perform an analysis that would help them identify distant galaxies by looking for objects that are present in some parts of the spectrum but missing in others.
The research was based on the understanding that for hundreds of millions of years after the formation of the Cosmic Microwave Background, most of the Universe was filled with hydrogen atoms. These would absorb any light at or above a wavelength sufficient to ionize the hydrogen, essentially making the Universe opaque to those wavelengths. Back then, that limit was somewhere at the UV end of the spectrum. But in the intervening time, the expansion of the Universe has shifted this cutoff to the infrared part of the spectrum – one of the main reasons Webb was designed to be sensitive to these wavelengths.
First you don’t see (left), then you see. Inverted luminosity images show an object highlighted with a crosshair, but only visible in a region of space at longer wavelengths.
So the team looked for objects that were in images of the lowest-energy parts of the infrared spectrum viewed by Webb, but not in the higher-energy parts. And the exact spot where it disappears is how redshifted the cutoff for that galaxy is, and therefore 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 furthest from them: GLASS-z13 and GLASS-z11. The former is even farther than the confirmed furthest distance of anything detected in the Hubble Deep Field; If confirmed, this would make it the most distant object we know of, and therefore the closest in time to the Big Bang.
