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

One of the design goals of the James Webb Space Telescope was to provide imaging capabilities at wavelengths that would reveal the universe’s first stars and galaxies. Now, a few weeks after its first images were revealed, we are getting clear indications that it has succeeded. In some data made public by NASA, researchers have discovered as many as five galaxies in the distant universe, which already existed a few hundred million years after the Big Bang. If confirmed to be as far away as they appear, they would be one of the most distant galaxies yet seen.

opening up
For many of its observatories, NASA allows astronomers to submit proposals for observations and then grants those users exclusive access to the resulting data for a period of time. But for its new tool, NASA has a set of goals where the data will immediately be made public, for anyone to analyze as they wish. Some of these include locations similar to the first images released, where a large cluster of foreground galaxies acts as a lens to magnify more distant objects.

(You can see details of one of the datasets used for this analysis, called GLASS, which used the cluster Abell 2744 to map out distant objects that were magnified by telescopes.)

The images in this dataset were long exposures at different parts of the infrared spectrum. The full range of wavelengths covered by the NIRCam instrument was divided 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 parts to analyze them to help them identify distant galaxies by finding objects present in some parts of the spectrum, but missing from others.

The discovery was based on the assumption 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 will absorb light at or above wavelengths sufficient to ionize hydrogen, essentially making the universe opaque to these wavelengths. At the time, this cutoff was somewhere in the UV end of the spectrum. But in the interim, the expansion of the universe moved that cutoff into the infrared part of the spectrum—a major reason why the Web was designed to be sensitive to these wavelengths.

So the team looked for objects that were present in images of the lowest-energy parts of the infrared spectrum imaged by the Web but were absent in the high-energy parts. And the exact point at which it disappears indicates how red-shifted the cutoff is for that galaxy, and thus how far away the galaxy is. (You can expect future research to take a similar approach.)

This method resulted in five different objects of interest, and the draft manuscript focuses on the two most distant of these: GLASS-z13 and GLASS-z11. The former distance is greater than the confirmed distance of anything seen in the Hubble Deep Field; If confirmed, this would make it the most distant object we know of and thus the closest to the time of the Big Bang.