Full-color images from NASA's James Webb Space Telescope

How the James Webb Space Telescope captures stunning images from space

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

The responsibility of translating Webb’s observations into jaw-dropping images for NASA rests largely on the shoulders of only two people: Alyssa Pagan, Science Visuals Developer, and Joseph DePasquale, Senior Data Image Developer, at the Space Telescope Science Institute (STSI) in Baltimore. Pagan described Webb and Hubble as giant eyes designed to absorb huge amounts of light using mirrors.

READ MORE: 5 awesome new images of the universe from the James Webb Space Telescope

“You might think of [the telescopes] like having huge pupils – their mirror size is like their pupil size,” Pagan explained. “So they’re like these light-gathering buckets, basically.”

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

Scientists can glean all kinds of information from the light captured by Webb, such as the elements that make up an observed object or its temperature. The telescope uses various filters to capture wavelength ranges primarily 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 the emission of cooler molecular gas or the emission of dust,” said Anton Koekemoer, a research astronomer at the Space Telescope Science Institute. PBS NewsHour via email.

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

It takes a few days on average to create the colorful images that NASA touts in press releases, but Pagan and DePasquale aren’t doing it alone. Researchers step in to ensure that the images highlight the scientific value of the observations. The data itself isn’t manipulated, just the details that catch your eye, like how adjusting a photo’s brightness or contrast doesn’t alter the basic scene it depicts.

“It’s this back and forth to make sure the science informs the picture and it illustrates the discovery,” Pagan said.

Here’s a look at the key differences between Webb and Hubble, along with a handful of Webb images — some of which Pagan has personally handled — and why the new insights they offer make them such valuable additions to the field of astronomy. .

How is Webb different 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 able to detect infrared light, especially in the near and mid range. Hubble can see visible light and ultraviolet light, plus a small fraction of infrared.

A phenomenon called redshift plays a huge role in what makes Webb’s infrared observations so important. The universe is constantly expanding, which means that the light that first emanated from stars and galaxies millions, if not billions of years ago, traveled through space for a very long time before reaching Webb’s giant mirrored eye. During this journey, what started out as visible or ultraviolet light stretched, slowly transitioning to infrared – hence the term “red shift”. That’s why Webb is uniquely positioned to observe some of the oldest and most distant objects the universe has to offer.

optical spectrum map-01 (1)

Graphic by Megan McGrew/PBS NewsHour

“It helps us go back in time – more – and better understand the early universe,” Pagan said. “It’s a lot about filling in the timeline and the different stages and different understandings of the objects and how they evolved.”

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

But to create the Webb images we see on Earth, Pagan and DePasquale must move this observed infrared light into the visible spectrum, a process she likened to transcribing music from one octave to another. To do this, both follow the rules of light in the visible spectrum – longer wavelengths are redder and shorter ones are bluer.

“We just assume, ‘Hey, maybe if we saw in infrared, we have the same kind of way of seeing,'” Pagan said. “So would we know exactly what those colors would look like if we had the ability to analyze color in the infrared? Not sure, but we certainly try 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 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 in this rusty dust.

“You’re basically seeing an evolutionary part or phase of the star that we don’t have [yet] figure out until we have more infrared capability,” Pagan said. “So it’s sort of filling out the star timeline, [whereas] with Hubble, we see more of it once it grows and hits the main sequence.

READ MORE: James Webb Space Telescope Shows Jupiter’s Auroras, Tiny Moons

This image was the first to be processed by Pagan. She said she wanted to emphasize the contrast between the two processes occurring in the image – the hot, fiery, mountain-like cloud of dust at the base of the image, and the sea of ​​stars and gas. sky-like hotspots at the top, radiating this dust below. Initially, the colors were closer to red and teal, but this combination did not suit Pagan. Going with a more blue and orange jumpsuit suited her eye better.

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

Webb can see more and more distant galaxies than Hubble because it is more sensitive and because of the redshift. This is why more galaxies dot the background of these five prominent galaxies. While the dust in Hubble’s image is quite dark, it’s completely bright in Webb’s, Pagan noted, helping researchers better understand the dust itself.

“It’s a different way of looking at it – where before the dust is a bit like a clouding 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 image on the right was taken with his Mid-Infrared Instrument (MIRI). While NIRcam allows us to see through the dust in this image, MIRI makes the dust itself more visible, offering two distinct looks at the same phenomenon, Pagan said.

Our deepest look at space yet

The sensitivity that distinguishes Webb from Hubble is particularly noticeable in their respective “deep field” shots, both of which are speckled with countless galaxies within the cluster known as SMACS 0723. Webb is the deepest, sharpest infrared image ever taken of the distant universe, and it also shows the faintest objects yet seen in this part of the light spectrum, according to NASA. Webb’s greater sensitivity and ability to pick up red-shifted light allows the focal points of the telescope’s image to “come alive,” Pagan said.

To have the role she plays – translating the clearest images of space that humanity has ever managed to capture, and acknowledging that she’s probably the first to see some elements of those observations – is both exciting and “overwhelming in a tremendous way,” Pagan said, adding that she felt honored and lucky to be in the right place at the right time to process many of the breathtaking new images of space that Webb has taken. so 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, it was a company over 25 years old. And here I am almost at the finish line to show what all this work was for. So, I better do a good job,” laughed Pagan. “But it was amazing.”

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