The James Webb Space Telescope (JWST) has returned to Hubble’s Ultra Deep Field, capturing more than 2,500 galaxies throughout cosmic history. It is part of the JWST Jade Survey, reliving the same patch in infrared light. Webb’s infrared cameras (Nircam and Miri) see much brighter objects than Hubble. While Hubble’s UDF showed about 10,000 galaxies in visible light, Webb’s extremely deep (~100 hours) mid-infrared exposures are now revealing galaxies that formed just a few hundred million years after the Big Bang. About 80% of the galaxies in Webb’s image are visible from this early era.
Sharper, deeper infrared imaging
According to a study published in the journal Astronomy & Astrophysics, Webb’s infrared instruments have dramatically sharpened the deep field. Its Mid-Infrared Instrument (MIRI) F560W filter—the longest single-filter exposure on Webb—used about 100 hours—while NIRCAM provides shorter-wavelength coverage. Together, they provide a multiwavelength infrared view “deeper than any previous survey,” surpassing the depth and richness of Hubble.
The new image covers about a quarter of the original UDF, but still contains ~2500 galaxies, many too faint for Hubble. In parallel, the Jade team used the Webb Nirspec spectrograph on 253 very faint sources, obtaining reliable redshifts and spectra for 178 of them (going out to z≈13.2).
Galaxies, star formation and hidden black holes
Webb’s false-color image encodes the distance and composition of each galaxy. Many galaxies glow red or orange, indicating dusty star-forming systems or older red populations of stars. These red/orange objects may also harbor active central black holes (active galactic nuclei) heating dust. Small greenish-white dots mark the most distant galaxies (visible within the first billion years), while blue/cyan spots are closer, lower-attenuation shift systems.
This color coding helps astronomers pinpoint where star formation is intense and where hidden black holes reside. The Jade program will then use NIRSPEC spectroscopy to measure the star formation rate and chemical makeup of each galaxy, creating a detailed census of the early universe.
