When the Hubble Space Telescope was aimed at a presumably empty spot in the sky for 10 days in 1995, astronomers were stunned to find some 3,000 never before seen galaxies, some dating back to the infancy of the cosmos. Subsequent “deep field” images pushed the threshold back even farther in space and time.
Now, with the James Webb Space Telescope, astronomers are observing the oldest galaxies ever detected. Providing a taste of deep field images to come, Webb took a brief look at the same area imaged in the Hubble Deep Field, using the infrared telescope’s NIRCam instrument. Hubble’s view took 11.3 days to capture. Webb needed less than one day to to detect galaxies of similar faintness.
The Webb data were not collected for a deep field project per se. Researchers were interested in using NIRCam’s medium-band filters to better understand star formation and ionisation in the first billion years after the Big Bang when the universe transitioned from neutral gas to an ionised state in the light of emerging stars and galaxies.
“I don’t know if I was surprised exactly, but the images were even better than I was expecting,” said Michael Maseda of the University of Wisconsin-Madison. “In these images, you can actually see by eye that this is ionised gas over a fairly large area. I was expecting everything to be unresolved, but we have a high-enough resolution to actually see it. And I’m pleased to see it because it could have been a lot harder to understand what was happening.”
Said NOIRLab’s Christina Williams: “I think that seeing how beautiful the images are and how high quality they ended up being was definitely a high point. We calculated that we would be able to do things like this, but it was different to see it and have the real data in practice.”