To appear in UoA Scientific Review, 2022 Issue 4.
Images from https://www.flickr.com/photos/nasawebbtelescope/albums/72177720300469752
In mid-July 2022, a million miles from Earth, the James Webb Space Telescope (JWST) entered service. Five unique test images highlighting the telescope’s various subsystems and capabilities were made available to the public in high-profile events from the governments of the USA and the European Union, garnering international coverage.
A month on, the scientific community has been hard at work to incorporate the latest JWST results into a wide range of research inquiries. In this briefly essay, we will look back at the first five images, and discuss their importance and the scientific potential they entail.
01. SMACS-0723 Deep Field (4 billion lightyears from earth, and far beyond)
To the uninitiated, it may have been confusing why this image was used to open the JWST announcement; it looked like a star field any night sky photographer or artist can produce. This is until you realise that the image is an extremely zoomed-in1 patch of the night sky: almost every spot of light2 here is a distant galaxy, and this image literally looks far beyond our galaxy, across the history of our universe. Discovered by the Southern Massive Cluster Survey project a decade ago, SMACS-0723 is a cluster of galaxies 4 billion light years away from earth, and they show up in this image in white. Everything else with a more reddish-orange hue is a galaxy further away.
You can see some orange arcs seemingly centred around the SMACS-0723 member galaxies. It sure feels odd that a galaxy has a structure like this, and they actually don’t. In truth, they only appear to us as distorted filaments because to the sheer mass of the foreground SMACS-0723 causes gravitational lensing. According to the theory of general relativity, heavy objects significantly warp the spacetime around them, even bending the light rays travelling past.
Such lensingeffects are important to astronomers. Not only can they demonstrate for us the power of general relativity, but allow us sometimes to “zoom in” on much more distant objects otherwise too dim even for JWST to see. In this picture, the oldest galaxy is established3 to be 13.1 billion years old — forming not long after the big bang was theorised to have taken place 13.8 billion years ago. We could see it because SMACS-0723’s gravitational field helped us, increasing the distant galaxy’s apparent luminosity by many orders of magnitude.
In another similar JWST image after this one, galaxies even farther away have been reported. The reddest one yet, GLASS-z13, clocks in at just 329.8 million years after the big bang. Due to the expansion of the universe, it has a present-day distance of 33 billion lightyears away from us. Such numbers provide long-awaited tests on our cosmological theories regarding the organisation of structures in the universe — when, and how, galaxies form out of the shimmering afterglow of the Big Bang, guided by dark matter or exotic physics we do not yet understand.
Lastly, when Hubble Space Telescope photographed SMACS-0723, it took almost a week to complete the exposure. JWST only took half a day, and reached a much higher image quality. I have prepared an interactive comparison web app you can play with at fwphys.com/jwsts-first-color-image/.
02. Stephan’s Quintet (290 million lightyears from earth)
Named after its discoverer, French astronomer Édouard Stephan (1837 – 1923), the “Quintet” is four galaxies locked in a collision course, with the fifth one (NGC 7320) much closer to earth (40 million light years) and just photobombing. Out of the five images released, this is the one closest to my research area as it looks into the intricate matter of galaxy mergers, and provide many exciting prospects.
The timescale of a galactic collision is justifiably beyond human comprehension. Though every star and jet of gas in this picture is moving at astonishingly high speed, over the span of thousands of human lifetimes, everything will look the same, frozen in a voyage across the vastness of space. Dynamically, we don’t the quintet reach its final act until billions of years in the future, when the galaxies are so thoroughly stirred up by each other, that they form a big elliptical galaxy, and their supermassive black holes eventually coalesce.
While we won’t be around to witness any of this, clever use of instrumentation aboard the JWST already provides us with much information about the fascinating array of processes that take place during a galactic merger.
The galaxies participating in the cosmic dance are referred to by astronomers as Hickson Compact Group 92 (HCG 92). Each of the four galaxies has a supermassive black hole in its centre, dominating the dynamics. Three of them are already so close to each other that long tidal tails, streams of stars and gas, can be seen ripped from their disks, inter-weaving with each other.
Thanks to JWST’s ability to observe in infrared, piercing through the shrouds of galactic dust, astronomers are given an opportunity to see in unprecedented detail how galactic collisions stir up gas and trigger the birth of new stars. Then, using the integral field unit (IFU), which effectively takes a spectrum of every pixel at the same time, JWST was able to produce magnetic resonance images of galactic structures, not unlike the technique you see in modern medical imaging. This allows astronomers to access a rich array of information, including the individual distribution of certain chemical compounds.
In addition, one of the member galaxies of HCG 92 harbours an active galaxy nucleus, driven by a very energetic central black hole. It is estimated to weigh 24 million solar masses, and emit radiation at 40 billion times our sun’s output power. JWST imaged the hot gas near the black hole and measured the velocity of bright outflows in a level of detail never seen before. This provides important insight into the properties of a supermassive black hole.
The imaging of NGC 7320 is not futile either. Thanks to its closer distance to earth, JWST was able to resolve its structure to an impressive extent, identifying individual stars, its bright core, and mapping the distribution of gas — star formation material. On the day of the image announcement, I remember seeing a tweet from a colleague in the US who works on galactic modelling. “It looks just like the simulations!”, he commented.
03. Carina Nebula (8500 lightyears from earth)
One of the “tourist attractions” within our own galaxy, the Carina Nebula is the largest nebula visible in the southern night sky. It is part of the open star cluster NGC 3324.
In the eye of JWST, the gaseous layers looked like a side of a mountain, and newly formed stars diamonds sprinkled onto the rocks. Of course, the heights of the hills are measured in lightyears, and the stars are all still very far apart.
The properties of these new stars, their number, masses and chemical composition, are all of research interest in astronomy today. Furthermore, JWST will not only study how galactic gas clouds give rise to new stars, but how these stars shape the gas clouds in return, the back-reaction. The intricate structures lining the expansive cliffs of gas is not only a snapshot of its innate dynamics, but also profoundly influencedth by the radiation and stellar winds of newly birthed stars nested within such a galactic nursery.
04. Southern Ring Nebula (2000 lightyears from earth)
In a poetic dual to how the previous two pictures were about stellar births, this one is a stellar funeral.
The southern ring nebula, NGC 3132, is located in the constellation Vela. It is a planetary nebula4, result of a series of bursts when a dying star gradually lost grasp on its outer shells, retaining only its core to become a white dwarf, a stellar remnant.
The southern ring nebula has been extensively studied for decades, and the new imagery shows the nebula’s central white dwarf in greater than ever detail. In addition, the binary nature of the system is confirmed, as another star closely bound to the white dwarf is also captured in this image. It’s of interest how the two stars shaped the nebula’s structure together.
Often described as a pool of light, its glow is driven by the remaining white dwarf’s intense ultraviolet radiation and stellar winds. As the white dwarf cools and the gas continues to expand, this structure will eventually lose its shape and colours, mixing with other galactic materials to give rise to the next generation of stars.
As a surprise to astronomers, to the left edge of the nebula is another case of cosmic photobombing. JWST was able to identify a far-away galaxy that faces us perfectly edge-on. Such occurrences are rather rare in the night sky, and is a meaningful addition to our stash of galactic profiles.
05. The Atmospheric Spectrum of WASP-96b (1150 lightyears from earth)
This one might have been the confusing outlier. “Where is the visual?” “What is this curve?”
In short, this image is the most detailed near-infrared transmission spectrum of an exoplanet atmosphere humanity has ever produced.
When the planet moves in front of its parent star, it partially blocks the starlight reaching us, and the planet’s atmosphere’s chemical makeup can be measured via transmission spectroscopy.
Discovered in 2013 in the Wide Angle Search for Planets project, WASP-96b itself is quite unlikely to harbour life. Categorised as a “hot Jupiter”, it has a similar mass to ♄ and encircles its sun-like parent star once every 3.4 Earth days, at a distance of only 11% Mercury’s orbital radius. Such an extreme set of orbital characteristics means it is permanently tidally locked to its parent star, with the bright side reaching temperatures upwards of 1000 ºC. However, this also provides an advantage to JWST with regards to technical demonstrations: it does not need to wait around for an observation window of WASP-96b, and measurements can be repeated rather quickly in the matter of days.
This JWST image also provided key insight into an ongoing debate. Owing to the planet’s uniquely sharp sodium absorption lines, some prior literature argued that this planet is without clouds. However, using a range wider than previous instruments, JWST found unambiguous signature of water, indications of haze, and evidence of clouds that were thought not to exist based on prior observations.
The spectroscopic range of JWST is particularly suited to look for atmospheric chemicals such as water, oxygen, methane, and carbon dioxide. Several dozen planetary targets, from giant planets to small earth-like rocky planets, are scheduled for observations. The ability to quickly and reliably produce such atmospheric spectra will be an important tool to aid our search for extraterrestrial life and habitable planets in the future.
Closing Remarks
At midnight on 26 December 2021, I watched James Webb Space Telescope launch out from French Guiana live on TV. I set up a camera beforehand to record my reactions, wanting to give a little speech marking the moment. In reality, I found myself at a complete loss for words as the Ariane rocket lifted off, and I froze in reverential silence.
With its scale and duration, and of course the final cost of 10 billion USD, the JWST is an awe-inducing mega project, and I pay my utmost respect for the scientists and engineers who worked on it. I remember reading about the James Webb Space Telescope, then “projected to launch in early 2006”, when I was just a school pupil. Between then and the eventual successful deployment, it — we, despite a mixed bag of emotions and experiences over the intervening years (division, warfare, economic collapses, environmental disasters, disease outbreaks, and so on), we have persisted.
The telescope is both a witness and a fruit of a time not without problems here on the ground. Although it will probably not send back any quick answers from up in space, it will push the human race forward.
In one of author Cixin Liu’s short stories, 朝闻道5, an advanced civilisation placed monitors on planets with intelligent life, to raise alarms in case one world quickly develops technology powerful enough to destroy the universe. When the aliens eventually knocked on the door of humanity, people asked them when the alarm was raised:
“Was it when we first detonated nuclear weapons?”
“Was it when we started radio broadcasts?”
“Was it when we invented controlled flight?”
…
“No,” the aliens said, bringing up a hologram of the Eastern African plains 370 thousand years ago, upon which a few shadows stood still in the landscape veiled in darkness.
“Here. A caveman looked at the night sky for too long, above our safety threshold. This is what triggered our alarm.”
Humans are a curious bunch on our humble planet, and much of our ability to shape our world roots in our collective pursuit of wonder. It is thus of my belief that the successful beginning of the JWST mission is a milestone in our history.
Our remote descendants will recount this year, these first results, with profound excitement and veneration: how the JWST first opened our eyes to so much of the cosmos so long hidden, how it inspired so many questions never asked before, and how it marked the beginning of our species’ eventual conquest of spaces.
Notes on False Colour Images
There are perhaps two kinds of casual astronomy readers, with very few in between: those who assume the universe appears to the human eye like the space telescope photos above, and those who categorically dismiss any such images, saying “they are all synthesised anyway”. Setting aside the problem of how little light the human eye can capture compared with specialised sensors, the colours themselves are a subtle subject.
To me, it is not redundant to always stress that astrophysical images are presented in “false colour” — so-called because the Red, Green, and Blue channels that make up an image are used to represent information measured originally in other frequencies (colours) of light.
The JWST, for example, owing to how far into the history of the universe it is designed to look, and also to reduce extinction effects due to dust in our own galaxy, is an infrared instrument, detecting light with wavelength between 600 to 28000 nanometres. Compared with the human eye’s preference, 380 to 700 nanometers, there isn’t much of an overlap.
Well, our vision has evolved for a long time for the express goal to suit our habitat, some lush grasslands on a tiny planet, lit by an ordinary G-type “yellow-white” star. It can then be argued that the universe has no obligation to mind such innate limitations of ours, and the use of false colours is a smart compromise when presenting the universe’s structures and dynamics. Therefore, some conversion methods were employed by scientists to visualise the officially published JWST data, and you can even develop your own false colour schemes to visualise the same data differently!
In summary, we cannot see the universe like in the images with our own eyes, ever, but it does not make the visualisations we produce with our instruments and computers any less valuable and impressive.
Footnotes
[1] There is a zoomable version on the Internet, showing how small this patch of sky really is, https://web.wwtassets.org/specials/2022/jwst-smacs/
[2] The ones with diffraction spikes are foreground stars situated within the milky way galaxy. They are distant and dim also, but no where near the distance of the galaxies in the photo.
[3] Accompanying this image, the JWST team later also released optical spectra of a few of the galaxies in it. Redshift can be reliably measured using the emission peaks of hydrogen. This was a very difficult task before JWST.
[4] The name “planetary nebula” is a historical artefact as the early telescopes could only roughly resolve their shapes, mistaking them for planets in the solar system. We now know that they have nothing to do with planets. In particular, the southern ring nebula is about half a lightyear wide.
[5] The story title is hard to translate directly as it is taken from a Confucius quote, “Should one learn the universe’s way in the morning, and die in the evening, there is no regret.” I am in the process of making an English version with the title “Morning. Truth.” You can see the draft here, fwphys.com/zwd_ch1/
References and Further Reading
JWST First Image Press Releases. https://www.nasa.gov/webbfirstimages
Garner, Rob (2022-07-08). “NASA Shares List of Cosmic Targets for Webb Telescope’s 1st Images”. NASA.
Naidu, Rohan P.; et al. (July 2022). “Two Remarkably Luminous Galaxy Candidates at z ≈ 11 − 13 Revealed by JWST”. arXiv:2207.09434
Pontoonidan, Klaus; et al. (July 2022). “The JWST Early Release Observations.” arXiv: 2207.13067
“Two Weeks In, the Webb Space Telescope Is Reshaping Astronomy”, Quanta Magazine https://www.quantamagazine.org/two-weeks-in-the-webb-space-telescope-is-reshaping-astronomy-20220725/
Nikolov, N., Sing, D.K., Fortney, J.J. et al. An absolute sodium abundance for a cloud-free ‘hot Saturn’ exoplanet. Nature 557, 526–529 (2018). https://doi.org/10.1038/s41586-018-0101-7