Are the James Webb Space Telescope’s Pictures ‘Real’?

Are the James Webb Space Telescope’s Pictures ‘Real’?

How the JWST’s cosmic images are made

Credit: Jen Christiansen (graphic); NASA, ESA, CSA, STScI and Webb ERO Production Team (image source)

As light travels through space, it gets stretched by the expansion of the universe. Infrared light is longer than visible light and is why many distant objects shine in it. We can’t see this ancient light with our eyes, but the James Webb Space Telescope (JWST) was designed to capture it, revealing some of the first galaxies ever to form.

Chart shows the electromagnetic spectrum range that humans can see, and the larger infrared portion that the JWST can detect.
Credit: Jen Christiansen

Integrated Science Instrument Module

JWST’s base includes four science instruments that collect its data.

Side view of JWST shows the position of the instrument module, behind the primary mirror.
Credit: Jen Christiansen

Six Data Collection Components . . .

Aperture Masking: A perforated metal plate blocks some of the light entering the telescope, allowing it to simulate an interferometer, which combines data from multiple telescopes to achieve higher resolution than a single lens. This technique allows you to see more detail of bright objects, such as stars close by.

Micro Shutter Array: A grid of 248,000 small doors can open or close to measure spectra–light spread into its constituent wavelengths–from up to 100 points in a single frame.

Spectrographs: Gratings or prisms separate incoming light into spectra to reveal the intensity of individual wavelengths.

Cameras: JWST has three cameras–two that capture light in the near-infrared wavelength range and one that works in the mid-infrared.

Integral Field Unit: A combined camera and spectrograph captures an image, along with spectra for each pixel, revealing how the light varies across the field of view.

Coronagraphs: Glare from bright stars can blot out fainter light from planets and debris disks orbiting those stars. Coronagraphs are opaque circles which block the bright starlight and allow weaker signals to pass through.

Six icons, representing aperture masking, micro shutter array, spectrographs, cameras, integral field unit, and coronagraphs.
Credit: Jen Christiansen

. . . Distributed across Four Instruments

Fine Guidance Sensor (FGS)/Near-InfraRed Imager and Slitless Spectrograph (NIRISS): The FGS is a guide camera that helps to point the telescope in the right direction. It comes with the NIRISS, which includes a camera and an spectrograph for taking images and spectra of the near-infrared spectrum.

Schematic of FGS and NIRISS. Components include aperture masking, spectrographs and cameras. Detects infrared up to 5 microns.
Credit: Jen Christiansen (graphic); NASA; ESA; STScI; Andi James and J. Olmsted, STScI (references)

Near-Infrared Spectrograph (NIRSpec): This dedicated spectrograph can capture 100 spectra simultaneously with its micro shutter array. This instrument is the first to be able to simultaneously take spectroscopy of multiple objects.

Schematic of NIRSpec. Components include micro shutter array, spectrograph and integral field unit. Detects up to 5 microns.
Credit: Jen Christiansen (graphic); NASA; ESA; STScI; Andi James and J. Olmsted, STScI (references)

Near-Infrared Camera (NIRCam): The only near-infrared instrument with a coronagraph, NIRCam will be a key instrument for studying exoplanets whose light would otherwise be drowned out by their nearby star’s glare. It will capture high resolution images and spectra of the near-infrared.

Schematic of NIRCam. Components include spectrograph, camera, and coronagraph. Detects infrared up to 5 microns.
Credit: Jen Christiansen (graphic); NASA; ESA; STScI; Andi James and J. Olmsted, STScI (references)

Mid-Infrared Instrument (MIRI): This combination camera and spectrograph is JWST’s only instrument capable of seeing in the mid-infrared, where cooler objects such as debris disks around stars and extremely distant galaxies emit their light.

Schematic of MIRI. Components include spectrograph, camera, integral field unit and coronagraph. Detects 5-28 microns.
Credit: Jen Christiansen (graphic); NASA; ESA; STScI; Andi James and J. Olmsted, STScI (references)

Are the Pictures “Real”?

Scientists must make adjustments to transform JWST’s raw data to something that human eyes can appreciate. But its photos are “real,” says Alyssa Pgan, science visuals development for the Space Telescope Science Institute. “Is this what we would see if we were there?” “No, our eyes aren’t built to see infrared and the telescope is far more sensitive than our eyes to light. This gives us a better representation of these cosmic objects than our limited eyes could. JWST can take images in up to 27 filters that capture different ranges of the infrared spectrum. Scientists first determine the most useful dynamic range to capture an image. Then they scale the brightness values to reveal the most details. Each infrared filter is assigned a color from the visible spectrum. The shorter wavelengths are assigned blue, while the longer wavelengths are assigned green and red. These are then combined to give you the usual white balancing, contrast, and color adjustments that any photographer might need.

Data from 4 infrared filters are stretched and assigned blue, green, orange or red. The composite is a full-color nebula image.
Credit: Jen Christiansen (graphic); NASA, ESA, CSA, STScI and Webb ERO Production Team (image source)

Data Details

Although the full-color images are stunning, many of the fascinating discoveries only show one wavelength. The NIRSpec instrument can reveal different features of Tarantula Nebula using different filters. The wavelength emitted by atomic hydrogen (blue), for instance, comes from a central star as well as from a bubble surrounding it. In between are the signatures of molecular hydrogen (green) and complex hydrocarbons (red). These data indicate that a cluster in the frame’s lower left is blowing a frontal of gas and dust towards the central star.

Data from 3 infrared filters are assigned colors. Blue is assigned to 1.87 microns, green to 2.12, and red to 3.3.
Credit: Jen Christiansen (graphic); NASA, ESA, CSA, STScI and Webb ERO Production Team (image source)

This article was originally published with the title “Behind the Pictures” in Scientific American 327, 6, 42-45 (December 2022)

doi: 10. 1038/scientificamerican1222-42

ABOUT THE AUTHOR(S)

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    Jen Christiansen is senior graphics editor at Scientific American. Follow Christiansen on Twitter @ChristiansenJen

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      Clara Moskowitzis Scientific American‘s senior editor covering space and physics. Follow Moskowitz on Twitter Schematic of NIRSpec. Components include micro shutter array, spectrograph and integral field unit. Detects up to 5 microns.

      2154331Clara Moskowitz is the senior editor for Scientific American Follow Moskowitz on Twitter @ClaraMoskowitz Credit: Nick Higgins

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