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Microshutters

What Webb’s Microshutters Do

The James Webb Space Telescope's microshutter array is a grid of 248,000 tiny doors that can be individually opened and closed to transmit or block light to capture spectra (think data!) of hundreds of individual objects in a field of stars or galaxies simultaneously. It delivers extremely detailed data about each object it observes, multiplying the science researchers can produce. The microshutter array is housed within Webb’s Near-Infrared Spectrograph (NIRSpec), a multifaceted scientific instrument that was developed by the European Space Agency (ESA). This technology was developed specifically for Webb: This is the first time an instrument like this has flown in space! How does the instrument work? What does it do? Here, we walk you through it step by step.

So Many, So Small

Quadrants with white outlines are centered against a black background. Below the bottom left quadrant is an outline of a stamp. An illustrated magnifying glass appears over the two quadrants on the right. Within the magnifying glass, three microshutters are enlarged. When looking again at the four quadrants, it becomes clear that each quadrant has very hazy outlines of hundreds of thousands of tiny microshutters.
There are 248,000 microshutters split into four quadrants. Each quadrant is the size of a postage stamp.

How It Works

Forty-two microshutters are shown, six across and seven down. Each microshutter is wider than it is tall and has black lines running from top to bottom. In the second row, the three shutters at the left are open. In the third row, three shutters at the right are open. An illustration of a half-circle representing a magnet on the right side of the graphic has open ends, which are facing the shutters. The ends of the semi-circle are red, and the top end has a plus sign and at the bottom a minus sign. Wavy blue lines extend from the magnet on the right to shutters on the left.
Magnets selectively open tiny doors all across the array, allowing the telescope's instruments to capture light (as spectra) from up to 100 celestial objects simultaneously.

Splitting Light

One open microshutter is at the top-center of the image. A four-pointed star is behind it. A triangular ray of light shines from the star, widening significantly to enclose two rainbows below it. The label 1D represents the top line that begins in red, transforms into yellow as it goes down into a valley, where it appears green. The green transforms into blue as the peak ascends, ending in purple near the bottom of the shutter above it. Below this, the label 2D appears left of a rectangular line with the exact same color pattern, except where the dips are in the 1D line, there are there are black lines in the spectrum.
Instruments behind Webb's microshutters spread light into colorful spectra, which help researchers learn about distant stars and galaxies.

What We Learn from Spectra

Five icons appear with one-word labels. Color is represented by a semi-circular rainbow at top left. Temperature is represented by a red thermometer at top center. Composition is represented by the element hydrogen at top right. Motion is represented by a yellow circle with lines bottom left. Mass is represented by a blue kettlebell bottom right.
Spectra break light into its component wavelengths, revealing clues about the state, temperature, speed, distance, and composition of stars and galaxies.

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In-Depth Example: Galaxies

What We Learn by Looking at Galaxies’ Light

Spectra tell us an immense amount about galaxies, including very distant galaxies as they existed in the early universe. In the graphs below, we’ve plotted the light gathered from three spiral galaxies. The large black arrows at the left of each spectrum emphasize how far the light from each galaxy has redshifted, or stretched into longer, redder wavelengths due to the expansion of the universe, before reaching the telescope.

The first sample spiral galaxy at the top is the closest to Earth. Its light existed a mere 480 million years after the big bang, which happened more than 13.8 billion years ago. The light observed in the second shows it as it existed only 420 million years after the big bang. The third is the most distant. Its light reflects this spiral galaxy as it existed only 370 million years after the big bang. Although the light from each galaxy was redshifted, we still observe the galaxies as they were when that light was emitted—when the galaxies were young. By comparing galaxies that existed at various times in the universe we can understand how they change over time.

Webb’s microshutter array is not only designed to capture these longer wavelengths of light, known as infrared, but will also be able to accurately sample the light from each galaxy simultaneously to help researchers identify their type (spiral, elliptical, or irregular), their distances from Earth, their ages, and their redshifts.

Three graphs are stacked on top of one another horizontally to show variations in the brightness of light from three spiral galaxies. See extended description for detail.

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The Full Field of Galaxies

In the image below, Webb's full image of galaxy cluster SMACS 0723 is at left. Webb’s image is approximately the size of a grain of sand held at arm’s length, a tiny sliver of our vast universe. The smallest, reddest smudges are the most distant galaxies, but there are galaxies of all types and shapes, including spiral, elliptical, and irregular galaxies. By using Webb’s microshutter array, researchers can learn more about the masses, ages, histories, and compositions of galaxies in this field.

Of the thousands of distant galaxies behind galaxy cluster SMACS 0723, the microshutters were used to observe 48 individually, all at the same time. Quick analysis made it immediately clear that several of these galaxies were observed as they existed at very early periods in the history of the universe. Light from the farthest galaxy shown traveled 13.1 billion years before Webb’s mirrors captured it. With these observations, Webb showed us the chemical composition of galaxies in the very early universe for the first time.

An infographic titled “Galaxy Cluster SMACS 0723, Webb Spectra Identify Galaxies in the Very Early Universe; NIRCam Imaging and NIRSpec Microshutter Array Spectroscopy.” The infographic shows the redshift of four distant galaxies. At left is a NIRCam image of the field, which is filled with galaxies of different colors, shapes, and sizes. Four galaxies from this image are highlighted, and labeled: 11.3 billion years, 12.6 billion years, 13.0 billion years, 13.1 billion years to indicate when the observed light was emitted. In inset images, these galaxies appear blurry and have red areas. To the right are four line graphs corresponding to the four highlighted galaxies. These are labeled NIRSpec Microshutter Array Spectroscopy. They show the shift in the position of hydrogen and oxygen emission lines to longer wavelengths as age of the light increases.

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