One of the design goals of the James Webb Space Telescope was to provide the ability to take 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 are getting a strong indication that it is a success. In some of the data released by NASA, scientists have seen as many as five galaxies from the distant universe, already present just a few hundred million years after the Big Bang. If confirmed to be as distant as they appear, one of them would 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 some time afterwards. But for its newest instrument, NASA has a set of goals where the data will be made public immediately, allowing anyone to analyze as they wish. Some of these include locations similar to one of the first images released, where a large cluster of galaxies in the foreground acts as a lens to magnify more distant objects.
(You can look at the details in one of the datasets used for this analysis, called GLASS, which used the cluster Abell 2744 to magnify distant objects, which were further magnified by the telescope.)
The images in this data set were long exposures made at different parts of the infrared spectrum. The full spectrum of wavelengths covered by the NIRCam instrument was divided into seven parts, and each part was imaged for anywhere from 1.5 to 6.6 hours. A large international team of researchers used these bits 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 from others.
The search 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 all 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 at the UV end of the spectrum. But in the intervening time, the expansion of the universe pushed this limit into the infrared part of the spectrum—one of the main reasons Webb was designed to be sensitive to these wavelengths.
So the team looked for objects that were present in the images of the lowest-energy bits of the infrared spectrum imaged by Webb, but absent from the higher-energy clumps. And the exact point where it disappeared indicates how redshifted the boundary is for that galaxy, and thus how distant the galaxy is. (You can expect future research to involve 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 more distant than the farthest confirmed distance of anything detected in the Hubble 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.