Jul 17, 2022 - Science

How the James Webb Space Telescope's images are made

The Carina Nebula seen by the James Webb Space Telescope

The Carina Nebula as seen by the James Webb Space Telescope. Photo: NASA, ESA, CSA, and STScI

Hours of image processing work went into each of the five full-color James Webb Space Telescope images released by NASA this week.

Why it matters: Through its photos, the JWST — which captures light in wavelengths the human eye can't see — will change the way the public and scientists understand the history of the universe.

Where it stands: The JWST looks at the universe in infrared light, allowing it to cut through dust to see the intimate details of star formation and even the faint light of some of the first galaxies that formed more than 13 billion years ago.

  • "Biologically, we just don't have the ability — even if we were floating next to these objects — to see them the way that Hubble or Webb can see them," Joe DePasquale, an image processor who works with JWST, tells Axios.

How it works: When photos taken by the JWST's huge mirror are beamed back to Earth, they basically look black, DePasquale says.

  • "Each pixel in the image has over 65,000 different shades of gray that it can be," he said, adding that "the universe is very dim," so most of the interesting parts of a JWST image are "buried in the darkest regions of the image."
  • The imaging team then has to brighten up the darkest parts of the image to bring out the details hiding within the pixels without over-saturating the brightest bits of the image — which can be cores of galaxies or bright stars.

The JWST is so sensitive that it's able to differentiate between bands of infrared light in much the same way our eyes can see different bands of optical light — which we perceive as colors.

  • Because of that sensitivity, the imaging team is able to sort through long to short wavelengths of infrared light, allowing them to filter the image through various colors in a scientifically sound way.
  • The human eye perceives longer wavelengths of optical light as red, so that color stands in for longer wavelengths of infrared light. Blue is used for shorter wavelengths and the other colors of the rainbow are in between.
  • "If you had infrared eyes that were sensitive to this light, this may be what you would see," Klaus Pontoppidan, a JWST project scientist said during a press conference.
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