JWST sees light invisible to the eye. These scientists decide how to color it

In terms of appearances, the universe is a tough place. Seen gentle occupies merely a sliver of the electromagnetic (EM) spectrum. To review the cosmos in its entirety, scientists should peer past seen gentle utilizing specialised devices, together with radio telescopes and X-ray telescopes. And the James Webb House Telescope (JWST) senses infrared (IR) radiation, piercing by way of dusty veils that block seen gentle.

The researchers and builders who’re tasked with processing these information are offered with a singular problem: What colour is gentle that people can’t see? It takes a stunning mixture of artwork and science to reply this query and convey these cosmic scenes to life.

The method of deciphering information from non-optical telescopes is commonly referred to as false colorization, however the phrase “false” does it a disservice. The approach has been used for many years to render colour images from uncooked information, together with in a few of Hubble’s most well-known photographs, which mix the telescope’s optical capabilities with its ultraviolet (UV) and IR information. Similar to every other digicam, this processing creates footage from in any other case meaningless sequence of zeroes and ones.

“Consultant colour is a extra correct time period,” says Joe DePasquale of the House Telescope Science Institute (STScI) in Baltimore, Maryland, the place JWST and its imagery are managed. As considered one of solely two space visuals builders at STScI, DePasquale is obsessed with dispelling any public skepticism bred by the time period “false colours.”

“It’s a delicate mix of artwork and science, leaning extra towards the science,” he explains. “We work with scientists to make aesthetic judgments and spotlight key scientific options with out altering the information. The entire level is to indicate what the telescope observes in the easiest way attainable.”

Nothing false about false colour

The method of consultant colorization includes assigning colours primarily based on relationships patterned after human perceptions of seen gentle. Since JWST detects gentle in near- and mid-IR bands, that vary of wavelengths should be shifted — or mapped, as picture processors name it — into the seen colour space.

“Assigning colours is fairly effectively established,” says Alyssa Pagan, STScI’s different space visuals developer. Usually, this remapping follows the identical order because the seen portion of the spectrum, “making the shortest wavelengths bluer, and the longer wavelengths redder,” she explains. “However there’s a number of flexibility. We are able to make the center wavelengths barely extra cyan or inexperienced simply to get fuller colour illustration.”

JWST’s completely different filters — 29 within the mid-IR and 10 within the near-IR — reveal completely different features of an object’s construction. A nebula could have filaments of dust overlapping with clouds of sizzling gasoline, every of that are accentuated by completely different wavelengths. Changes are made to focus on these options.

“You do your finest to both subtract or improve,” says Pagan. “Regardless that scientists would possibly use six filters to get a picture, you don’t essentially need to use all of them. That may neutralize options that overlap, like mixing an excessive amount of paint and getting brown. You need to watch out, however you need to get the most important colour gamut you’ll be able to.”

Spanning the spectrum

In addition to JWST, astronomers make use of a broad array of observatories to see the remainder of the EM spectrum. Beginning with low-energy radio waves and shifting as much as microwaves, then IR, UV, X-rays, and eventually gamma rays, these telescopes reveal the unimaginable, together with the cosmic microwave background left over from the Massive Bang, supermassive black holes, the interior constructions of nebulae, and exploding supernovae. (One key observatory on this fleet, the Chandra X-ray Observatory, was just lately tagged for retirement by a NASA committee with no substitute on the horizon — to the dismay and protests of scientists.)

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Though the identical fundamental guidelines apply in deciphering information from this various vary of telescopes, combining their information throughout the EM spectrum is difficult. However the outcomes — generally known as multi-wavelength photographs — may be spectacular and revealing.

Pagan compares the method to making an attempt to mix a traditional picture of a human arm with X-rays of the bones inside. “They don’t match up very effectively, however you’ll be able to assign one colour in your X-ray and one other in your pores and skin to see what’s actually taking place. It’s like plotting a graph with 5 completely different colours to indicate completely different numerical info.”

Visualizations for the general public eye

Again in spring 2022, within the leadup to the revealing of JWST’s first scientific photographs, STScI gave itself a brief window of time to pick and render a number of the most spectacular targets the telescope had imaged as much as that time. “The crew met every day for six weeks,” DePasquale says. “We had scientists, writers, graphic designers, after which Alisa and myself.”

The ensuing photographs turned immediately iconic. Pagan labored on the Cosmic Cliffs — the nickname the crew gave to a billowing wall of gasoline and dust surrounding the star cluster NGC 3324, close to the Carina Nebula. DePasquale tackled the Tarantula Nebula (30 Doradus), an enormous stellar nursery within the Giant Magellanic Cloud, amongst others.

DePasquale says he doesn’t take the duty of colorization — or its impression — without any consideration. “It’s a tall order deciphering what we get from a telescope and creating the imagery that shapes the general public’s notion of the universe.”

If you wish to attempt your personal hand at consultant colorization, STScI makes JWST information and software program out there on the mission’s website. For extra info, try Warren Keller’s story in our September difficulty on easy methods to course of your personal JWST photographs.