These images highlight the gigantic advance JWST provides for mid-infrared astronomy (wavelengths 5 to 25 microns). Only a fraction of this wavelength range can be observed from the ground where we contend with huge infrared fluxes from both the telescope and atmosphere, requiring that we measure astronomical sources contributing sometimes no more than 0.001% of the total flux received by the detectors. This handicap was overcome for the first time with the Infrared Astronomical Satellite, launched in 1983 and, in the vacuum of space, cooled to near absolute zero. Its deep observations are still mined as a fundamental resource 40 years later.

Credit: NASA/Andras Gaspar, University of Arizona

A series of cold space telescopes followed — ISO, Spitzer, Akari, WISE — each a benchmark in the field. But what they gained in sensitivity, they lacked in resolution; their small telescopes, ranging from 40 to 85 centimetres in aperture, were severely limited by diffraction. Only large ground-based telescopes, with their limitations in sensitivity, could deliver sub-arcsecond resolution images. Infrared astronomers could only envy the exquisite high-resolution yet very sensitive observations obtained routinely at other wavelengths.

JWST, as another cold telescope in space, provides a wonderful advance in sensitivity. However, at least as important are the far sharper images delivered by its 650-centimetre aperture. With a beam area 50 times smaller than any previous cold space telescope, mid-infrared astronomy has entered a new era when the detailed structures of sources can be explored. This breakthrough is illustrated in this image of a dense star field within the Large Magellanic Cloud, showing the same field and at similar wavelengths as seen by the 40-centimetre WISE telescope (left), the 85-centimetre Spitzer one (middle), and the 650-centimetre JWST (right), using the Mid-Infrared Instrument. What a revelation! We were euphoric when we saw that our dreams of beautiful, clear mid-infrared images had just become a reality!