Get ready for a new way to see the universe

The James Webb Space Telescope (JWST) is NASA’s next major observatory; in line with the Hubble Space Telescope, the Compton Gamma-Ray Observatory, the Chandra X-Ray Observatory and the Spitzer Space Telescope. JWST combines the qualities of two of its predecessors, observing in infrared light, like Spitzer, with fine resolution, like Hubble. Credit: NASA, SkyWorks Digital, Northrop Grumman, STScI

James Webb Space Telescope is finally ready to do science – and it’s seeing the universe more clearly than even its own engineers hoped for.

NASA is scheduled to release the first images taken by the James Webb Space Telescope on July 12, 2022. They’ll mark the beginning of the next era in astronomy as Webb – the largest space telescope ever built – begins collecting scientific data that will help answer questions about the earliest moments of the universe and allow astronomers to study exoplanets in greater detail than ever before. But it has taken nearly eight months of travel, setup, testing, and calibration to make sure this most valuable of telescopes is ready for prime time. Marcia Rieke, an astronomer at the University of Arizona and the scientist in charge of one of Webb’s four cameras, explains what she and her colleagues have been doing to get this telescope up and running.

1. What has happened since the launch of the telescope?

Following the successful launch of the James Webb Space Telescope on December 25, 2021, the team began the long process of moving the telescope to its final orbital position, unfolding the telescope, and – as everything cooled – calibrating the cameras and sensors. onboard sensors.

The launch went as smoothly as a rocket launch can get. One of the first things my NASA colleagues noticed was that the telescope had more fuel on board than expected to make future adjustments to its orbit. This will allow Webb to operate much longer than the mission’s original 10-year goal.

The first task on Webb’s month-long journey to its final location in orbit was to unfold the telescope. It went off without a hitch, starting with the blank deployment of the sunshade that helps cool the telescope, followed by aligning the mirrors and activating the sensors.

Once the sunshade was opened, our team began monitoring the temperatures of the four onboard cameras and spectrometers, waiting for them to reach temperatures low enough that we could begin testing each of the 17 different modes the instruments can operate in. function.

NIR Cam

The NIRCam, seen here, will measure infrared light from extremely distant and ancient galaxies. It was the first instrument to come online and helped align the 18 mirror segments. Credit: NASA/Chris Gunn

2. What did you test first?

Webb’s cameras cooled as the engineers had predicted, and the first instrument the team turned on was the Near Infrared Camera – or NIRCam. NIRCam is designed to study the faint infrared light produced by the oldest stars or galaxies in the universe. But before it could do that, NIRCam had to help align the 18 individual segments of Webb’s mirror.

Once NIRCam cooled to minus 280 F, it was cool enough to begin detecting light reflected from Webb’s mirror segments and producing the telescope’s first images. The NIRCam team was thrilled when the first bright image arrived. We were in business!

These images showed that the mirror segments were all pointing to a relatively small area of ​​the sky, and the alignment was much better than the worst-case scenarios we had anticipated.

Webb’s fine guidance sensor also entered service at this time. This sensor helps keep the telescope pointed steadily at a target, much like the image stabilization in consumer digital cameras. Using the HD84800 star as a reference point, my colleagues from the NIRCam team helped dial in the alignment of the mirror segments until it was near perfect, far better than the minimum required for a successful mission. .

3. Which sensors then came to life?

As the mirror alignment wrapped up on March 11, the Near Infrared Spectrograph – NIRSpec – and Near Infrared Imager and Slitless Spectrograph – NIRISS – finished cooling and joined the party.

NIRSpec is designed to measure the strength of different wavelengths of light coming from a target. This information can reveal the composition and temperature of distant stars and galaxies. NIRSpec does this by looking at its target object through a slit that blocks all other light from entering.

NIRSpec has multiple slots that allow it to look at 100 objects at once. Team members started by testing the multi-target mode, commanding the slits to open and close, and they confirmed that the slits responded correctly to commands. The next steps will measure exactly where the slits are pointing and verify that multiple targets can be observed simultaneously.

NIRISS is a slitless spectrograph that also breaks down light into its different wavelengths, but is more efficient at observing all objects in a field, not just those on the slits. It has several modes, including two specially designed to study exoplanets particularly close to their parent stars.

So far, instrument checks and calibrations have gone smoothly, and the results show that NIRSpec and NIRISS will deliver even better data than what engineers predicted before launch.

Webb MIRI and Spitzer Comparison Image

The MIRI camera, image on the right, allows astronomers to see through dust clouds with incredible clarity compared to previous telescopes like the Spitzer Space Telescope, which produced the image on the left. Credit: NASA/JPL-Caltech (left), NASA/ESA/CSA/STScI (right)

4. What was the last instrument to light up?

The last instrument to start on Webb was the Mid-Infrared Instrument, or MIRI. MIRI is designed to take pictures of distant or newly formed galaxies as well as small faint objects like asteroids. This sensor detects the longest wavelengths of Webb’s instruments and should be kept at minus 449 F – only 11 degrees F above[{” attribute=””>absolute zero. If it were any warmer, the detectors would pick up only the heat from the instrument itself, not the interesting objects out in space. MIRI has its own cooling system, which needed extra time to become fully operational before the instrument could be turned on.

Radio astronomers have found hints that there are galaxies completely hidden by dust and undetectable by telescopes like Hubble that captures wavelengths of light similar to those visible to the human eye. The extremely cold temperatures allow MIRI to be incredibly sensitive to light in the mid-infrared range which can pass through dust more easily. When this sensitivity is combined with Webb’s large mirror, it allows MIRI to penetrate these dust clouds and reveal the stars and structures in such galaxies for the first time.

5. What’s next for Webb?

As of June 15, 2022, all of Webb’s instruments are on and have taken their first images. Additionally, four imaging modes, three time series modes and three spectroscopic modes have been tested and certified, leaving just three to go.

On July 12, NASA plans to release a suite of teaser observations that illustrate Webb’s capabilities. These will show the beauty of Webb imagery and also give astronomers a real taste of the quality of data they will receive.

After July 12, the James Webb Space Telescope will start working full time on its science mission. The detailed schedule for the coming year hasn’t yet been released, but astronomers across the world are eagerly waiting to get the first data back from the most powerful space telescope ever built.

Written by Marcia Rieke, Regents Professor of Astronomy, University of Arizona.

This article was first published in The Conversation.The Conversation

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