How the James Webb Space Telescope captures stunning images of space

The James Webb Space Telescope has offered mesmerizing new shots of the cosmos — from nebulae to galaxies to the early universe — since its first set of images was revealed in July. Webb is a successor to the still-active Hubble Space Telescope, which launched in 1990. The two are designed to observe different swaths of the electromagnetic spectrum, meaning they each deliver valuable information about celestial phenomena in unique ways.

The responsibility of translating Webb’s observations into jaw-dropping images for NASA largely rests on the shoulders of just two people: science visuals developer Alyssa Pagan and senior data imaging developer Joseph DePasquale at the Space Telescope Science Institute (STSI) in Baltimore. Pagan described both Webb and Hubble as akin to giant eyes built to take in massive amounts of light using mirrors.

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“You could think of [the telescopes] as having huge pupils — their mirror size is like their pupil size,” Pagan explained. “So they’re like these buckets of light collectors, essentially.”

Webb is larger and more sensitive than Hubble — the area of its mirror is more than five times greater than its predecessor’s, which allows it to capture dimmer light from more distant objects, according to the STSI. But both are valuable tools that can offer astronomers different types of information, much like an X-ray and an MRI reveal different details about a person’s body, Pagan said.

Scientists can glean all sorts of information from the light that Webb picks up, like which elements comprise an observed object or how hot it is. The telescope uses various filters to pick up wavelength ranges mostly in the infrared, Pagan said.

“For example, some filters are at wavelengths corresponding to hot ionized gas, while other filters are at wavelengths corresponding to emission from colder molecular gas, or emission from dust,” Anton Koekemoer, a research astronomer at the Space Telescope Science Institute, told the PBS NewsHour via email.

Researchers like Koekemoer often stitch together separate images taken through these filters to create a kind of mosaic before passing them along to Pagan and DePasquale for processing.

It takes an average of a few days to create the colorful images that NASA touts in press releases, but Pagan and DePasquale aren’t doing it all alone. Researchers chime in to make sure that the images emphasize the scientific value of the observations. The data itself isn’t manipulated, just the details that your eye is drawn to, like how tweaking the brightness or contrast of a photograph doesn’t alter the basic scene it depicts.

“It’s that back and forth of making sure that the science is informing the image, and that it’s illustrating the discovery,” Pagan said.

Here’s a look at the main differences between Webb and Hubble, plus a handful of Webb images — including some that Pagan personally processed — and why the novel information they offer makes them such valuable additions to the field of astronomy.

How does Webb differ from Hubble?

Webb’s giant mirror can be compared to our pupils, but that’s about where the similarities to human eyes end. Our eyes can only see the visible spectrum, while Webb is capable of detecting infrared light, specifically in the near and mid range. Hubble can see visible light and ultraviolet light, plus a small fraction of infrared.

A phenomenon called redshifting plays a huge role in what makes Webb’s infrared observations so significant. The universe is ever-expanding, which means that the light that first emanated from stars and galaxies millions or even billions of years ago traveled across space for a very long time before reaching Webb’s giant mirrored eye. During that journey, what started off as visible or ultraviolet light has stretched out, slowly shifting into infrared — hence the term “redshift.” That’s why Webb is uniquely suited to observe some of the oldest and most distant objects the universe has to offer.

Chart by Megan McGrew/PBS NewsHour

“It helps us see way back in time — more — and get a better understanding of the early universe,” Pagan said. “It’s a lot about filling the timeline and different stages and different understandings of objects and how they evolve.”

Webb is equipped with several tools to make these observations possible. Its near-infrared camera (NIRCam) peers through dust to get a glimpse of the celestial landscape beyond. The telescope’s mid-infrared camera (MIRI) takes things a step further, Pagan said, by capturing infrared light emitted from dust so that it can become the focus of an image instead of an obscuration. Both of these capabilities set it apart from Hubble.

But in order to create the Webb images we see back on Earth, Pagan and DePasquale have to shift that observed infrared light into the visible spectrum, a process that she compared to transcribing music from one octave to another. To make this happen, the two follow the rules of light in the visible spectrum — longer wavelengths are redder and shorter ones are bluer.

“We’re just assuming ‘Hey, maybe if we saw in infrared, we have that same sort of way of seeing,’” Pagan said. “So would we know exactly what those colors would look like if we had the ability to parse color in infrared? Not sure, but definitely we’re trying to use the physical meaning that we see in visible light.”

A dusty Carina Nebula

Comparing images of this slice of the Carina Nebula — a region dubbed NGC 3324 — shows just how many stars were obscured by dust in Hubble’s view. The new Webb image will help researchers better understand the process of star formation, which occurs within that rusty dust.

“You’re basically seeing an evolutionary part or phase of the star that we did not [yet] understand until we had more infrared capability,” Pagan said. “So it’s kind of filling in the timeline of stars, [whereas] with Hubble, we see more of once it’s grown and hit the main sequence.”

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This image was the first one Pagan processed. She said she wanted to emphasize the contrast between the two processes happening in the image — the hot, fiery mountain-like cloud of dust at the base of the image, and the sky-like sea of stars and hot gas at the top, irradiating that dust below. Initially, the colors were closer to red and teal, but that combination didn’t sit well with Pagan. Going with a more blue and orange combination better suited her eye.

“There are artistic principles to it, too, that you kind of have to follow [when] you’re just like, ‘This just doesn’t read,’” Pagan said. “And the thing is, after they’ve done the objective part, [someone] might have a different conclusion. And like that’s part of the fun, I suppose, is that there are different ways to represent the data.”

In Stephan’s Quintet, a concert of dust and galaxies

Comparing Webb’s and Hubble’s respective shots of Stephan’s Quintet gives two good examples of what Webb has to offer: more galaxies and lit-up dust.

Webb can see more numerous and distant galaxies than Hubble because it’s more sensitive, and because of redshifting. That’s why more galaxies pepper the background of these five prominent galaxies. While the dust in Hubble’s image is fairly dark, it’s completely illuminated in Webb’s, Pagan noted, which helps researchers better understand the dust itself.

“It’s a different way of seeing it — where before, the dust is kind of like obscuring but you can’t really make it out, and then now, the dust is emitting [light],” she added.

Different slices of infrared light can tell us two different stories about Stephan’s Quintet. The image on the left was taken using Webb’s near-infrared camera (NIRCam), and the one on the right was taken with its mid-infrared instrument (MIRI). While NIRcam lets us see through the dust in this image, MIRI makes the dust itself most visible, offering two distinct looks at the same phenomenon, Pagan said.

Our deepest look at space yet

The sensitivity that sets Webb apart from Hubble is particularly notable in their respective “deep field” shots, both of which are speckled by countless galaxies within the cluster known as SMACS 0723. Webb’s image is the deepest and sharpest infrared image ever taken of the distant universe, and it also shows the faintest objects yet observed in that part of the light spectrum, according to NASA. Webb’s greater sensitivity and its ability to pick up redshifted light allow the foci of the telescope’s image to “come to life,” Pagan said.

To have the role that she does — translating the clearest images of space humanity has ever managed to take, and recognizing that she’s likely the first one to see certain elements of those observations — is both exciting and “overwhelming in a great way,” Pagan said, adding that she felt honored and lucky to be in the right place at the right time to process several of the novel, breathtaking images of space Webb has taken thus far.

“As I was processing the image, it brings tears to your eyes, because you’re like, ‘Oh, my God, all the things that people had to overcome to put this in space.’ I mean, this was a 25-plus-year endeavor. And here I’m at almost the finish line of showcasing what all this work was for. So, I better do a good job,” Pagan laughed. “But it was amazing.”