The farthest known galaxy candidate discovered by the James Webb Space Telescope

Two regions of the galaxy cluster Abell 2744, whose gravity magnifies light from extremely distant background galaxies. The colors are composed of several infrared images and the large fields are 2 arc minutes wide, which corresponds to 1/16 the width of the full moon. The close-ups show the galaxies GLASS-z10 and GLASS-z12, where the latter is a candidate to be the most distant galaxy ever discovered. Credit: NASA, ESA, CSA, Tommaso Treu (UCLA), Zolt G. Levay (STScI).

Less than a week after the James Webb Space Telescope was ready for science, the first reports of galaxy discoveries at record distances, and consequently in record times, appeared in preprints. Even more remarkable, these galaxies appear to be so massive that they challenge our understanding of how structure forms in the universe.

Now the first two of these reports have undergone mandatory peer review and have been accepted for publication in the scientific journal. The letters of the astrophysical journal, which corroborates the robustness of the result. However, astronomers are still waiting for the conclusive evidence: spectroscopy.

Just five days after the James Webb Space Telescope began its science observations in July, the first reports of record-breaking galaxies appeared. Not yet in scientific journals, but on the preprint server where researchers, eager to publish their results, often upload their manuscripts at the same time they submit them to journals.

Although the articles had not yet gone through the peer review process, which is so crucial to science, they naturally attracted media attention.

Observations challenge theories

The reason was not just that the now explored universe had grown in size. What’s more intriguing is that galaxies apparently harbor many more stars than we thought were possible. In fact, the foundations of our understanding of how massive structures accumulate over time are called into question; the “standard cosmological model”.

“From a theoretical point of view, the observed masses are quite puzzling,” explains Charlotte Mason, Associate Professor at the Cosmic Dawn Center (DAWN) in Copenhagen. “We would expect that we would have to search a much, much larger volume of space before finding galaxies that large. The average galaxy simply shouldn’t have had time to accumulate so much mass in the short time between the Big Bang and the time we see them.”

Mason co-authored one of the first two papers that have now been accepted for publication. This work, led by Marco Castellano at INAF Osservatorio Astronomico di Roma, reports the detection of several record-breaking distant galaxies.

The report appeared in preprint simultaneously with another paper, led by Rohan Naidu at MIT, which looked at the same field in the sky and found several of the same galaxies.

The candidate for the most distant galaxy ever seen, called GLASS-z12, through two different infrared filters that transmit light at 1.5 and 2.0 micrometers, respectively. The white bars mark the position of the galaxy and the darker colors represent more light. Because the galaxy’s short wavelengths are absorbed by the surrounding gas, it is virtually invisible through the 1.5 µm filter. This allowed astronomers to estimate its distance. Credit: . Naidu, P. Oesch, et al.

A fairly robust result

As detailed in a recent press release from the Cosmic Dawn Center, the technique used to determine the distances is a fast, but somewhat unreliable method, known to sometimes mistake the closest galaxies (or even local stars) for the very distant To confirm the distance, each galaxy must be followed with the more time-consuming spectroscopy, where the exact wavelength of each photon is measured.

Despite the lack of spectroscopy, the distances of two of the galaxies, named GLASS-z10 and GLASS-z12, appear fairly unambiguous. And the fact that two different teams, using two different analyzes of the same data, found the same distance is reassuring.