One of the design goals of the James Webb Space Telescope was to capture images at wavelengths that would reveal the universe’s first stars and galaxies. Now, just a few weeks after the first images were revealed, we’re getting a strong indication that it’s a success. In some data made public by NASA, researchers have seen as many as five galaxies of the distant Universe, which have been around several hundred million years after the Big Bang. If they are confirmed to be as far away as they seem, one of them will be the most distant galaxy yet observed.
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For many of its observatories, NASA allows astronomers to submit proposals for observation and then gives those users exclusive access to the resulting data for a period of time. But for its latest instrument, NASA has a set of targets where the data is immediately made public for anyone to analyze as they see fit. Some of these include locations similar to one of the first released images, where a large foreground galaxy cluster acts as a lens to magnify more distant objects.
(You can see the details of one of the datasets used for this analysis, called GLASS, which the cluster Abell 2744 used to magnify distant objects, which was further magnified by the telescope.)
The images in this dataset were long exposures taken on different parts of the infrared spectrum. The full range of wavelengths covered by the NIRCam instrument was divided 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 conduct 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.
The search was based on the insight that 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 rendering the universe opaque to these wavelengths. At the time, this limit was somewhere in the UV end of the spectrum. But in the intervening time, the expansion of the Universe shifted that frontier toward the infrared part of the spectrum — one of the main reasons the Webb was designed to be sensitive to these wavelengths.
At first you don’t see it (left), then you do. Inverted brightness images show an object appearing in a region of space marked by a crosshair, but only at longer wavelengths.
So the team looked for objects that were present in the images of the lowest energy chunks of the infrared spectrum imaged by Webb, but were absent in the higher energy chunks. And the precise point at which it disappeared indicates how redshifted the boundary is for that galaxy, and thus how far away the galaxy is. (You can expect future research to include a similar approach.)
This method yielded five different objects of interest, and a draft script focuses on the two most distant of these: GLASS-z13 and GLASS-z11. The first is even further away than the furthest confirmed distance from anything spotted in the Hubble Deep Field; if confirmed, this would make it the farthest object we know of and thus the closest to the Big Bang.
