Are the James Webb Space Telescope Images “Real”?

As light travels through space, it is stretched by the expansion of the universe. Because of this, many of the most distant objects glow in infrared light, which has a longer wavelength than visible light. We can’t see this ancient light with our eyes, but the James Webb Space Telescope (JWST) was designed to capture it and reveal some of the first galaxies to ever form.

Credit: Jen Christiansen

Integrated scientific instrument module

The core of JWST includes four scientific instruments described below that collect its data.

Credit: Jen Christiansen

Six Data Acquisition Components . . .

Aperture Masking: A perforated metal plate blocks some of the light entering the telescope, allowing an interferometer to be simulated that combines data from multiple telescopes to achieve higher resolution than a single lens. The technique shows more details of very bright objects close together, such as B. Two nearby stars in the sky.

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

Spectrographs: Gratings or prisms break down incident light into spectra to show the intensity of individual wavelengths.

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

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

Coronagraphs: Glare from bright stars can obliterate fainter light from planets and debris discs orbiting those stars. Coronagraphs are opaque circles that block bright starlight to let fainter signals through.

Credit: Jen Christiansen

. . . Spread over four instruments

Fine Guidance Sensor (FGS)/Near-InfraRed Imager and Slitless Spectrograph (NIRISS): The FGS is a guidance camera that helps point the telescope in the right direction. It is packaged together with the NIRISS, which has a camera and spectrograph to take images and spectra in the near infrared.

Photo credits: Jen Christiansen (graphic); NASA; ESA; STScI; Andi James and J. Olmsted, STScI (References)

Near-Infrared Spectrograph (NIRSpec): This special spectrograph can acquire 100 spectra simultaneously with its micro-shutter array. It is the first space instrument capable of spectroscopying so many objects simultaneously.

Photo credits: Jen Christiansen (graphic); NASA; ESA; STScI; Andi James and J. Olmsted, STScI (References)

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

Photo credits: Jen Christiansen (graphic); NASA; ESA; STScI; Andi James and J. Olmsted, STScI (References)

Mid-Infrared Instrument (MIRI): This camera and spectrograph combination 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.

Photo credits: Jen Christiansen (graphic); NASA; ESA; STScI; Andi James and J. Olmsted, STScI (References)

Are the pictures “real”?

Scientists have to make adjustments to turn the raw data from JWST into something the human eye can see, but its photos are “real,” says Alyssa Pagan, a developer of science visualizations at the Space Telescope Science Institute. “Is that what we would see if we were there? The answer to that is no, because our eyes are not built to see in the infrared, and also the telescope is much more sensitive to light than our eyes.” In that sense, the telescope’s improved view gives us a more accurate representation of how these cosmic objects are like look than our relatively limited eyes could. JWST can capture images in up to 27 filters that capture different parts of the infrared spectrum. Scientists first isolate the most useful dynamic range for a given image and scale the brightness values ​​to unlock the most detail. Then they assign each infrared filter a color from the visible part of the spectrum – the shortest wavelengths going blue and the longer wavelengths moving to green and red. After adding these together, all that’s left are the normal white balance, contrast, and color adjustments that any photographer could make.

Photo credits: Jen Christiansen (graphic); NASA, ESA, CSA, STScI and Webb ERO production team (image source)

data details

Though the full-color images are captivating, many of the exciting discoveries reveal one wavelength at a time. Here, the NIRSpec instrument shows different features of the Tarantula Nebula through different filters. For example, the wavelength emitted by atomic hydrogen (blue) comes from both a central star and a bubble surrounding it. In between are the signatures of molecular hydrogen (green) and complex hydrocarbons (red). The data indicate that a star cluster in the image’s lower right is blowing a front of dust and gas toward the central star.

Photo credits: Jen Christiansen (graphic); NASA, ESA, CSA, STScI and Webb ERO production team (image source)