James Webb Space Telescope Discovery

JWST image of the HH212 protostellar jet

Image and text by Mark McCaughrean, a senior scientist working with JWST data. This is a colour-composite infrared image of the highly-symmetric HH212 protostellar jet and outflow on the outskirts of the Orion B molecular cloud, as made using the NIRCam instrument on the NASA/ESA/CSA James Webb Space Telescope. A symmetric series of knots and bowshocks can be seen emerging to the left and right from an invisible protostar near the centre of the image. The jet extends over 0.5 parsecs or 1.6 light years in this image, although in wider-field pictures, further bowshocks are seen to the left and right, extending the flow overall to 2 parsecs. Comparison of the JWST image with ground-based data dating to 2000 show that the jet is expanding at roughly 100-150 kilometres per second. From this, a rough age of 7,000 years can be deduced for the outflow, although the protostar is likely to be older. The protostar is hidden by a dense circumstellar disk and envelope, but these are fairly limited in extent, as is evident from the many galaxies seen scattered across the field: if the molecular cloud core was large, they would be blocked from view. Extended mosaics of images were taken in six NIRCam filters, three medium-band and three narrow-band filters, as follow: F210M (H2 line emission at 2.12 microns & continuum); F212N (H2 line emission at 2.12 microns); F335M (H2 line emission at 3.23 microns & polycyclic aromatic hydrocarbon emission at 3.3 microns); F460M (H2 line emission at 4.69 microns, CO bandhead emission, & continuum); F466N (CO bandhead emission); F470N (H2 line emission at 4.69 microns). F210M & F212N were combined as blue; F335M as green; F466N as yellow; F460M & F470N as red. As the HH212 outflow is mostly emitting in shocked H2 lines, it is a red-purple colour, with colour differences due to variations in excitation and extinction, and with some yellow emission from CO. The widely-extended PAH emission from dust in the region is green. HH212 lies at a distance of roughly 400 parsecs from the Sun and is about 1.6 degrees NNE of the Horsehead Nebula in Orion. The original data were taken on 7 November 2022 and this composite image was released in November 2023. Data processing and image compositing done using the JWST pipeline, astropy, IRAF, GIMP, G'MIC-Qt, LightRoom, & PhotoShop. Credit: NASA, ESA, CSA, Mark McCaughrean & Sam Pearson, CC BY-SA HH 212
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