Graham writes …
After decades of development, and 6 months of launch, deployment, orbit acquisition and commissioning, the JWST is finally ready for action. It was on the 12th of July 2022 that NASA/ESA/CSA (1) released the first science results of the new space observatory, and these received significant media attention. In what follows, I will give a brief overview of the science revealed in the new images. For direct access to these and future images, and their interpretation, you can find the JWST image gallery by clicking here.
One of the most striking is the first JWST deep field image, as shown below. To acquire this, the telescope is pointed at a fixed position on the celestial sphere for an extended period. The Hubble Space Telescope (HST) acquired similar deep field images, but these took multiple weeks of stable pointing to build the images. This first JWST deep field was achieved in less than a day, and this is mainly because of two factors – the light gathering area of the JWST mirror is nearly 8 times more than that of the HST, and the JWST is optimized to operate in the infra-red (IR) part of the spectrum.
In previous blogs I have discussed what the IR optimization means, but it’s worth a brief recap. As you may recall, the IR part of the spectrum corresponds to heat radiation, as you can experience when sitting by a well-stoked open fire. It may appear strange to design the telescope to operate in this part of the electromagnetic (EM) spectrum, until one realises that we ‘see’ very distant objects – such as the first stars and galaxies – in this part of the spectrum. When these ancient objects formed, they generally emitted the peak of their radiation in the visible part of the EM spectrum. However, due to the expansion of the Universe, the fabric of space-time itself has significantly ‘stretched’, and by the same token so has wavelength of the emitted radiation. So all those interesting events that occurred just a few hundreds of millions of years after the creation event are most readily studied now by examining the IR part of the EM spectrum, which is at longer wavelength beyond visible red . See (2) for more detail.
The other advantage of using IR, as you may recall, is that the longer wavelength is scattered less by dust and debris, as illustrated by the accompanying images both acquired by the HST. The comparison shows the Carina Nebula in visible light (left) and infrared (right). The visible band image may be more pleasing aesthetically, but the infrared image is more revealing scientifically and, in this case, exhibits stars that weren’t visible before.
Getting back to the JWST deep field image, remarkably the angular size of the image on the sky is equivalent to the angle subtended by a grain of sand at arm’s length! So, all the stars (local to the Milky Way galaxy), galaxies and other features are all contained within a very small area of the sky. One can only try to imagine how many galaxies there may be across the entire sky. HST deep field images suggested a total of about 100 billion galaxies in the visible Universe, but it will be interesting to see what an updated JWST estimate may be. The other obvious features are the apparently distorted images of galaxies, that appear as stretched curved arcs of light. These are due to a phenomenon known as Einstein Rings, although in this case the rings are obviously fragmented. These are created when light from a galaxy or a star passes by a massive object on its way to the Earth. The massive object produces a gravitational lens which bends the light. If the source, lens, and observer are all in perfect alignment, the light appears as a ring, hence the name.
Clearly there are galaxies galore in this single image, many of which are billions of light years distant. One of the principal aims of the JWST project is examine the processes that led to the development and evolution of galaxies. To demonstrate the power of the JWST NIRSpec (Near Infra-Red Spectrometer) instrument, the science team identified a galaxy, the light from which has taken 13.1 billion years to reach us (recall that the Big Bang event is occurred around 13.8 billion years ago). Examining this light, the team produced the spectrum below, which features several prominent emission lines corresponding to its chemical composition. Please refer to the May 2022 blog post for more details of the JWST payload instruments.
Coming closer to home, the new observatory is also able to analyse the atmospheres of exoplanets – planets outside our own Solar System – using the NIRISS instrument (Near Infra-Red Imager and Slitless Spectrometer) to attempt to detect potential signatures of life elsewhere. The target test planet is about 1,150 light-years away located in the southern-sky constellation of the Phoenix. Designated ‘WASP-96 b’, it is a large, hot planet orbiting very close to a Sun-like star (and therefore not in the circumstellar habitable zone). As can be seen in the image below, the JWST spotted the unmistakable signature of water, signs of haze and evidence of clouds. Please note that the background image of a planet is there for purposes of presentation, and is not an image of WASP-96 b. But one thing that can be said, however, is that this is the most detailed exoplanet spectrum yet acquired.
Remaining within the Milky Way galaxy, at about 8,000 light years distance and in the Southern constellation of Carina (the keel), lies the Carina Nebula (NGC 3324). This remarkable object is a huge cloud of gas and dust which is effectively a stellar nursery. One of the first JWST images shows a small part of this nebula – see below. While taking a moment to appreciate the beauty and scale of the scene, it is also the case that it offers the science community the opportunity to examine the relatively ‘rapid process’ of stellar birth, which typically lasts only a few tens of thousands of years. In this image, previously hidden baby stars have been uncovered by JWST’s infra-red eye. In this type of object, the new telescope is able to reveal a significant number of such embryonic stars at different stages of their development, so allowing better understanding of the evolutionary process of stellar birth.
The next image is, again, of a ‘local’ object, the Southern Ring planetary nebula (NGC 3132) which is about 2,000 light years away in the southern sky constellation of Vela (the sails). The first thing to note is that planetary nebulae have nothing to do with planets. They are stars that have cast off a glowing ring of gas, which produces a roughly circular object. In the old days this disc-like object could be confused with the image of a planet. The JWST image below shows two views, using different payload instruments. The picture on the left was acquired using the NIRCam (Near Infra-Red Camera) instrument. In this part of the EM spectrum the image is closer to that which would be acquired in the visible band, showing off the surrounding stars and detail of the ejected gas and dust cloud. The image on the right was acquired using the MIRI (Mid Infra-Red Instrument), and at these longer wavelengths the telescope can penetrate some of the obscuring gas and dust to reveal that the central object is actually a binary star. The two stars orbiting around each other are very close, one being blue and the other red. It is likely that it was the red star that shed the gaseous layers to produce the overall disc-like image.
Finally, we go extra-galactic again in the last image of this initial release of JWST pictures - see below. This shows a feature called Stephan’s Quintet (NGC7318B - the brightest member), named after the astronomer who discovered it in 1877. This comprises five galaxies, four of which are gravitationally bound together. The galaxy on the left-hand side of the picture is actually much closer to us than the rest of the cluster. The four local members are about 290 million light years distant, in the northern sky constellation of Pegasus (the winged horse). The picture is a composite, built from about 1,000 JWST images in both the near and mid infra-red parts of the spectrum. The angular size of the image is about 1/5 the diameter of the moon (approximately 6 arc minutes) and also features foreground stars (local our own Milky Way galaxy) distinguished by the 8-spiked diffraction pattern. Remarkably, all the other objects in the image are very distant galaxies. I haven’t tried to count them but they must number in the hundreds.
I hope you have enjoyed this brief tour through the first JWST science images. It has certainly been worth waiting out the many years needed to bring the JWST project to fruition. Speaking as a scientist, I think they are awesome, and no doubt herald the beginning of yet another historic chapter in the annals of astrophysics and cosmology. There is a whole lot more to come in this story! As a Christian believer, the images bring into sharp focus the words of Psalm 19, verse 1: ‘The heavens declare the glory of God; the skies proclaim the works of his hands’(3). In my Christian journey, my first step, inspired by the science, was that I had become more comfortable with the idea of a creator God as the engineer of the observed fine-tuning of the cosmos (see (4) for more detail). By the same token, each time I experience the brilliance and warmth of the Sun on a beautiful summer’s day, that ‘gravitationally-bound fusion reactor’ in the sky brings home the notion of God’s creativity and power. In the same way, these new data from the JWST are an amazing reminder of God’s power and majesty. Wow!
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John Bryant and Graham Swinerd comment on biology, physics and faith.