What are the true colors of images from the James Webb Space Telescope?

By | March 26, 2024

NASAs James Webb Space Telescope (JWST) is known for capturing our universe with unprecedented precision and sensitivity. The images are not only scientifically useful, but also beautiful. From the blue and gold of the Southern Ring Nebula to the pink, orange and purple of Cassiopeia AJWST images depict the universe in brilliant colors.

The images are so stunning that you might wonder: do these cosmic objects really look so colorful? What would they look like if we could see them with our own eyes, instead of through a telescope?

“The quickest answer is: we don’t know,” says Alyssa Pagan, a science imagery developer at the Space Telescope Science Institute (STScI) and part of the team that adds color to the JWST images. But one thing is certain: you wouldn’t see the universe that way.

JWST is an infrared telescope, meaning it ‘looks’ at the universe with wavelengths of light longer than red light, which has the longest wavelength we can see with our eyes.

Related: How the James Webb Space Telescope’s infrared detectors will open new perspectives in astronomy

If you could look directly at these objects, you might see something closer to images from telescopes that rely on visual light, such as the Hubble Space Telescope, Heiden said. But even that comparison is not entirely correct, as Hubble is much larger and more sensitive than the human eye. In addition, visual light telescopes can capture different features of an image than an infrared telescope, even when pointed at the same target.

So how are the colors for these spectacular images chosen? JWST targets are viewed through several filters attached to the telescope that “see” a certain range of wavelengths of infrared light. JWST’s near-infrared camera, the telescope’s main camera, has six filters, each capturing slightly different images. By combining these images into a composite, Pagan and Joe DePasquale, another scientific visual developer at the STScI for JWST, can create the images in color.

When Pagan and DePasquale first receive the images, they appear in black and white. The colors are added to the image later as the data from the various filters is translated into the visible light spectrum, Pagan explains. The longest wavelengths appear red, while the shorter wavelengths appear blue or purple.

“We use that relationship with wavelengths and the color of light, and we only apply that to the infrared,” Pagan said.

Once each color has been added to the image, some additional changes may occur. Sometimes the original colors can make an image look faded or dusty, and the colors are made more vivid to make the quality sharper. The colors can also be shifted to emphasize certain hard-to-see features.

Pagan and DePasquale also work with researchers to ensure the images are scientifically accurate, especially when presented next to a particular scientific finding, Pagan said. Although the color images do not provide specific scientific data, they can help illustrate certain findings.

Sometimes they can also help scientists see areas they might want to investigate, Pagan said. For example, the most remote objects JWST’s first deep field recording – which appear red because the light traveling such a distance was stretched – presented targets for research into the early universe when these objects would have existed as they appeared in the deep field image.

The colors in JWST’s images may not be ‘real’, but you won’t get the wrong idea: the colors are not intended to deceive you, and they are not chosen just to look good. The images are intended to represent as clearly as possible what JWST can see – and what our eyes cannot see.

“We’re just trying to improve things to make it scientifically digestible and more attractive,” Pagan said.

The iconic pillars of creation.  The Hubble Space Telescope view on the left, the new photo from the James Webb Space Telescope on the right.

The iconic pillars of creation. The Hubble Space Telescope view on the left, the new photo from the James Webb Space Telescope on the right.

You can see some differences between images from visual light and infrared telescopes by comparing images of the iconic ones Pillars of Creation created by JWST and Hubble. While large parts of the pillars appear dark red in the Hubble image, the JWST image shows most of the formation in gold and orange hues. This means that the visual light emitted by the pillars has a longer wavelength (red), but is slightly closer to the center of the spectrum of infrared light shown in the image.

Much of the hazy material surrounding the pillars in the Hubble image, and even some of the materials of the pillars themselves, is also missing from the JWST image, meaning this portion of gas and dust is transparent in infrared. The JWST image also highlights more areas of star formation in red, which are obscured by thick clouds of gas and dust in the Hubble image.

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