An engineering image acquired during testing of one of James Webb Space Telescope's instruments reveals hundreds of distant galaxies in the deepest ever glimpse into the infrared universe.
The image, released by NASA on Wednesday (July 6), was captured by the James Webb Space Telescope's Fine Guidance Sensor (FGS) over an eight-day period in May and encompasses 72 snapshots taken during 32 hours of exposure time. Notably, the FGS, which was built by the Canadian Space Agency, is not a science instrument and instead keeps the observatory pointing properly at its target.
Still, the stunning image provides a taste of what's to come when the most powerful and expensive space observatory ever built finally commences its ambitious science work in earnest. The telescope is wrapping up commissioning and the Webb team is set to reveal the first truly science-grade images on Tuesday (July 12) at 10:30 a.m. EDT (1530 GMT) during a broadcast you can watch live here at Space.com.
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FGS took the false-color image during a "roll" test, according to a NASA statement about the image. While Webb's near-infrared camera focused on a star dubbed HD147980, the telescope rolled from side to side like an aircraft. During the test, the FGS kept the telescope pointed at its target. The resulting image, a byproduct of this support work, reveals the cosmos in a color scale from white to red, with whiter shades representing objects emitting the brightest infrared light and redder hues revealing dimmer objects.
"The faintest blobs in this image are exactly the types of faint galaxies that Webb will study in its first year of science operations," Jane Rigby, Webb's operations scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in the statement.
The image is not perfect, as it shows signs of the so-called dithering effect, which leaves black dots at the centers of the imaged stars. Dithering happens when the telescope slightly adjusts its position between exposures, which results in saturation of its detectors.
FGS's primary purpose is not to take scientific images, NASA said in the statement, and most of its photos will be discarded shortly after acquisition. The instrument's task is to enable accurate measurements by other instruments by helping the telescope to precisely point at the stars and galaxies the scientists are interested in. Still, the images hint at the ground-breaking discoveries that are to come from the observatory.
"When this image was taken, I was thrilled to clearly see all the detailed structure in these faint galaxies," Neil Rowlands, an FGS program scientist at Honeywell Aerospace, which built the instrument, said in the statement.
Since FGS was not designed primarily to do science, it doesn't use color filters like the other science instruments, which means scientists can't accurately determine the age of the galaxies in this image, the statement said.
Although the image may be the deepest of the infrared universe ever seen by the public, its glory won't last long as, according to NASA Administrator Bill Nelson, the July 12 release is set to contain the deepest image of the universe ever captured.
The James Webb Space Telescope carries two cameras and two spectrometers, which capture the light spectra of the imaged objects, revealing their chemical compositions. The telescope was specifically designed to see infrared light to detect some of the most distant (and oldest) galaxies in the universe. Although these galaxies emit visible light, due to the redshift effect caused by the expansion of the universe, this visible light shifts into the longer infrared wavelengths, which require an ultracold telescope like Webb.