Distant Galaxies Spotted by James Webb May Not Be So Distant Due to Errors

The James Webb Space Telescope is so good at capturing ancient light that some early discoveries may now need a “second look,” one scientist says.
The James Webb Space Telescope is so good at capturing ancient light that some early discoveries may now need a “second look,” one scientist says
JWST wide field image. Image:


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A month ago, space enthusiasts around the world were treated to the first spectacular views of our universe captured by the James Webb Space Telescope (JWST), the most powerful observatory ever launched. 

Since then, the JWST team has released incredible images of dying stars, cartwheeling galaxies, and the ancient universe. Astronomers, who have been waiting for this data for decades, have published a flurry of new research based on the unprecedented observations, including potential discoveries of galaxies that are farther back in time and space than ever seen before. 


However, some of these exciting initial claims might be errors associated with the calibration process of this complex observatory, which could throw off a crucial measurement known as redshift, reports a team led by Nathan Adams, a research associate at the Jodrell Bank Centre for Astrophysics. 

Redshift describes the way that light stretches into longer wavelengths as it travels across vast distances, which makes the dim glow of distant objects appear more red when it reaches instruments such as JSWT. Adams and his colleagues analyzed JWST’s new shots of  “ultra-high-redshift galaxies” that existed more than 13 billion years ago, according to a study published on the preprint server arxiv, which has not yet been peer reviewed. 

Their results clashed with some recent studies of these far-flung galaxies for an interesting reason: JWST is better at examining the distant “high redshift” universe by about 20 percent, compared to predictions.

“This could be quite a big deal for the high redshift science that has garnered a lot of attention in this first month of JWST data,” Adam told Motherboard in an email. “It is likely that this 20 percent overestimation of how bright these objects were in the redder wavelengths will affect the redshifts (distances) and masses that we estimated for these galaxies.” 

“We don't know for sure yet, but everyone will likely need to have a second look at what they've done so far.”


This epic astronomical nerdout has been exhilarating, but some of the finer details of the telescope’s calibration process may have been overlooked in the midst of the excitement. Adams noted that the researchers who are in charge of the telescope’s daily operations issued an early report that JWST’s Near Infrared Camera (NIRCam) instrument is so good at capturing red wavelengths that this part of the spectrum appears brighter than expected in its images. 

“JWST is a brand new instrument and we're still trying to get to grips with understanding how to process the data and what it means,” Adams said. “When the first images came out, it was a bit of an ‘astronomers at Christmas’ scenario with everyone diving in to see what they could find.”

“What I think flew under the radar of a lot of astronomers was that a part of that report mentions that NIRCam (one of the main cameras on the telescope) was overperforming in its reddest wavelengths,” he continued. “This is good news in the long term as it means we can go deeper than originally expected towards the redder wavelengths of light, however there was a catch for the short term that many missed.” 

“The analysis pipeline that had been made for JWST didn't account for that overperformance until an update on 2022-07-29, and so instead many people were measuring galaxies to be brighter in the redder wavelengths by approximately 20 percent than they really were for the first few weeks,” Adams said.


As a result, many objects appear bright in red wavelengths in these images because of JWST’s specs, not because they actually are extraordinarily distant and old. Adams and his colleagues pointed to studies that had reported objects that existed fewer than 200 million years after the Big Bang. It may be that these galaxies truly are that old and distant, but the new study suggests that this may only be a quirk of the observatory itself.

“Since we were finding more galaxies with very high redshifts /distances (you may have seen the numbers redshift 16 or 20 thrown around) than expected, and also seeing galaxies that were bigger in mass than we would have thought, this unaccounted-for error might be the reason why,” Adams said. 

In other words, everyone is seeing red, but how those wavelengths are actually interpreted will continue to be a work-in-progress as JWST tests its observational limits. Given the intricate and complicated nature of the telescope, it will take months to tweak all of its abilities, leaving astronomers to spar about the details in the meantime.  

“Even before the above issue was fully realized, many people were disagreeing about what galaxies in the images really were at these very high redshifts/distances (and subsequently, were being observed very early on in the Universe's history),” Adams said. “Everyone was using different methods to process the data, different models for the light that was being emitted from the galaxies etc. and there was some debate about which way was the more correct or reliable.” 

“Only 20-30 percent of the distant objects being found so far have more than one team in agreement with the same answers,” he noted. “But this 20 percent over estimation in how bright things were in the reddest wavelengths of light would be present in what everyone has done so far. I wanted to be clear that this wasn't just another paper with one team disagreeing with another team, but something everyone should be aware of.”

Like any instrument, musical or scientific, JWST will take time and practice to master. The early rush of studies has provided a tantalizing glimpse of what the telescope might reveal, and the process of working out the kinks in the system is, itself, part of the adventure.

“When we get spectroscopy, I have little doubt that some of these galaxies we thought were very high redshifts will turn out not to be,” Adams concluded. “But with that solid answer to hand, we can begin the process of figuring out why and refining our techniques. After all, that's what science is about!”