The James Webb Space Telescope (JWST) is performing better than expected, and that might be a problem for some of the early results. An update to our understanding of how one of its cameras is working may mean that many galaxies spotted in the early data are not as distant as they seem.
When JWST sends data back to Earth, it doesn鈥檛 come as complete images. Astronomers have to process it to make it usable, which requires understanding the sensitivity of the telescope鈥檚 scientific instruments. As JWST takes more data, we gain a better understanding of that sensitivity. But new information on the performance of an infrared camera caused the telescope鈥檚 operators to update its data-processing algorithms in July 鈥� well after the first images were released 鈥� and this threw some astronomers into a tizzy.
鈥淲hen the first images came out, it was a bit of an 鈥榓stronomers at Christmas鈥� scenario with everyone diving in to see what they could find,鈥� said at the University of Manchester, UK, in a statement. 鈥淲hat I think flew under the radar of a lot of astronomers was a part of that report mentions that NIRCam (one of the main cameras on the telescope) was overperforming in its reddest wavelengths.鈥�
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This is important because astronomers use the colour of an object鈥檚 light to measure its distance. The faster a galaxy is moving away from us, the redder its light appears. Because of the expansion of the universe, more distant galaxies move away from us faster, making them appear redder. Adams and his colleagues re-analysed some early JWST data after the update and found that some galaxies are actually less red 鈥� and correspondingly less distant 鈥� than they initially appeared.
鈥淚t鈥檚 potentially a very big deal,鈥� says at the University of California, Los Angeles. 鈥淭he data that we got is revolutionary and is great, but our understanding of the data is not.鈥� It may mean that some of the early science coming from JWST data is incorrect, especially for the faintest galaxies, where luminosity and distance are determined with fewer data points than brighter galaxies. Some faint galaxies may be more than 10 times closer than we thought.
However, that doesn鈥檛 apply to everything. 鈥淭his whole clamour of 鈥榦h my god, everything that everyone has written in the last few weeks is wrong, throw it out the window鈥� is really not the case,鈥� says at the Harvard-Smithsonian Center for Astrophysics. 鈥淭his is not unexpected, and many researchers made conservative choices in their work to account for it.鈥� For work focusing on very bright galaxies in particular, the corrections聽that need to be made to researchers鈥� calculations may not be all that extreme, he says.
It may even solve one mystery from the early data: the fact that JWST鈥檚 first observations聽seemed to show far more extremely distant galaxies than we expected based on models of galaxy evolution. 鈥淭his unaccounted for error might be the reason why,鈥� said Adams. If those galaxies aren鈥檛 quite so far away, the tension between theory and observation evaporates.
鈥淭his helps with part of the tension, but doesn鈥檛 completely solve it,鈥� says Roberts-Borsani. 鈥淭here are still these bright monsters at high distances where we don鈥檛 really expect them to be forming stars like crazy.鈥� Those bright galaxies aren鈥檛 affected as much by the updated NIRCam calibration.
More calibrations will come through from the JWST team in the coming months, but they鈥檙e all expected to be less severe, said Adams. Meanwhile, astronomers who analysed JWST data before this update are going back to double-check their conclusions. 鈥淥f course in the long run we鈥檙e going to iron all this out,鈥� says Naidu.
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