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Morning.

Here it is, several thousand years in the making: the protostellar jet HH212 as seen in the infrared by .

We discovered this jet in 1993, glowing in the light of shocked molecular hydrogen at 2.12 microns, as gas emerges symmetrically at about 100 km/s from the two poles of a young protostar not far from the Horsehead Nebula in Orion.

Our new JWST image spans six wavelengths & is ten times sharper than any previous infrared image.

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For scale, the image is about 0.7 parsecs or 2.3 light years wide at the 400 parsec distance to HH212, which lies on the outskirts of the Orion B molecular cloud, about 1.5° NE of the Horsehead Nebula near the Belt of Orion.

The full JWST image is over 11,000 pixels wide and can be viewed in detail and downloaded at full resolution from my Flickr account:

flic.kr/p/2pde2Nn

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FlickrJWST image of the HH212 protostellar jetBy Mark McCaughrean

To guide the eye, here’s a rotated and annotated version of the JWST image of HH212.

It shows the location of the central (invisible) protostar and then the quasi-symmetric series of knots and bowshocks caused by periodic expulsions of material from both poles of the protostar.

There are two other protostars in the region marked in blue.

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The image is a colour composite of six individual mosaics made through different medium & narrow-band filters with the NIRCam instrument on JWST:

F210M: H2 2.12 microns line + continuum (blue)
F212N: H2 2.12 microns line (blue)
F335M: H2 3.23 microns line + polycyclic aromatic hydrocarbon band (green)
F460M: H2 4.69 microns line + CO bandhead + continuum (red)
F466N: CO bandhead (yellow)
F470N: H2 4.69 micron line (red)

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With that colour mix, the jet is mostly red/purple as it is dominated by the various molecular hydrogen emission lines, energised by shocks in the outflowing material. There is also some CO emission in the flow & colour differences arise due to different excitation & dust extinction conditions, especially near the centre where there is lots of dust around the central protostar.

The diffuse green emission is due to polycyclic aromatic hydrocarbon emission associated with tenuous dust.

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Despite all this gas & dust however, we know that the protostar at the heart of HH212 is a fairly isolated, not surrounded by big dense molecular clouds.

How do we know that?

Because there are galaxies *everywhere* in this image, strewn across the image in the far distance.

If there was a dense cloud, we wouldn’t see them.

Here’s a small crop showing a nice group: pan & zoom & you’ll see loads more.

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We (Hans Zinnecker, John Rayner, & me) first discovered HH212 in 1993 using the NASA IRTF on Maunkea in Hawai’i.

We’ve observed it many times since on increasingly large telescopes & with better & better infrared cameras & better resolution, including the Calar Alto 3.5m in Spain & the ESO VLT 8.2m on Paranal, Chile.

Safe to say though, the images blow all that away 🙂👍

Here’s a montage with HH212 oriented “correctly”, ie with north up & east left.

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And to show the change in quality over time, here’s the previous best image of HH212, which we made with the VLT about 20 years ago, just in the 2.12 micron H2 line, compared with the new JWST image.

Pretty impressive improvement when you get to use a 6.5m cryogenic infrared telescope in space 🙂👍

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Mark McCaughrean

But here’s the thing: because we have all of these older images of HH212 … we can see it moving 😱

That is, because the material is moving outwards from the protostar we can see the jet expand over time.

It’s easily visible in this 22 year timelapse that combines three VLT images from 2000, 2007, 2018, & then the 2022 JWST image.

Measuring the changes, we can determine the expansion speed as 50-150km/s in different parts of the outflow.

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Here are some more full-resolution screen grabs to show the detail in the centre of the jet, in the bowshocks, and the other protostars in the region.

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And finally for now, here’s the redoubtable Mr Amos at the BBC with his take on our image of HH212, as well as the partner image we took with JWST of another protostellar outflow, HH211, which was published in Nature a few weeks ago.

We’re working on a paper about HH212 now as well, as you might imagine 😬👍

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bbc.com/news/science-environme

Close up of the telescope image of HH212
BBC News · James Webb telescope: Baby star launches giant jets and shocks - BBC NewsThe James Webb observatory records the giant jets and shocks created by a birthing star in Orion.

Ah, and of course, credit for these JWST images go to:

NASA/ESA/CSA/ Mark McCaughrean & Sam Pearson, CC BY-SA

Credit also to STScI & the NIRCam team for the pipeline processing tools, astropy & IRAF (yes, I’m old school), plus GIMP, @gmic, Adobe PhotoShop, & Adobe LightRoom which were used to make the images.

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As a coda, it’s important to note that HH212 has been studied intensively by many others since we discovered it, including a whole series of impressive papers looking at the inner jet & circumstellar disk by Chin-Fei Lee & Claudio Codella & their respective collaborators, using ALMA at millimetre wavelengths.

There’s amazing detail down in the region near the core where we’re blocked by dust, but they see the jet being launched by magnetic fields.

We’ll cite all that work in our paper 👍

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@mathildeD_V My pleasure – thanks for the positive feedback 🙂

@markmccaughrean These image descriptions are a great added value to this thread. For someone like me who doesn't know about astronomy, it's hard to understand what I'm actually seeing on the images, but it makes more sense with the alt texts. 👍

@maxi Thank you. There’s certainly more to be said which should help further explain what’s being seen in these images & why it’s important, so I’ll probably post some more notes later on 👍

@markmccaughrean Amazing thread and images and explanations, thank you!

@c_9 My pleasure – thanks for reading through it. There’s a lot more to be said about HH212 (& I forgot to mention that it extends considerably further on both sides, albeit not covered by JWST this time), so look out for the paper when we submit it.

@markmccaughrean The improved resolution of JWST is amazing.

@JanPV Indeed. The VLT data are pretty good for ground-based & the 2018 VLT image even used ground-layer laser AO, but it’s hard to beat a fully diffraction limited telescope in space, even if it’s smaller than each VLT unit telescope.

A laser guide star driven 39m ELT will be something though: might be worth returning again to HH212 with that in a few years 🙂👍

@markmccaughrean So not much worse than a storm off the Dutch coast then😂

@tanepiper What’s a factor of 3600 between friends, eh? 🙂