If the phrase “My god, it’s full of stars” was ever appropriate, it’s today, because of these new images from the James Webb Space Telescope. These are ‘just’ engineering images, mind you, but they are incredible. The number of stars and galaxies visible in each image is just remarkable, not to mention the crisp clarity in the fields of view.
The images were taken by JWST after the completion of the process to fully focus the telescope’s mirror segments. Now the team will begin commissioning the four science instruments, a process that will take about two months to complete. This is the final phase before the observatory will be fully ready to begin its science observations.
In analyzing these new images, the team says the optical performance is better than “the most optimistic predictions.”
“These remarkable test images from a successfully aligned telescope demonstrate what people across countries and continents can achieve when there is a bold scientific vision to explore the universe,” said Lee Feinberg, Webb optical telescope element manager at NASA’s Goddard Space Flight Center.
The alignment of the telescope’s 18 mirror segments means the mirrors are now directing fully focused light down into each instrument, and each instrument is successfully capturing images with the light being delivered to them. The teams said the image quality delivered to all instruments is “diffraction-limited,” meaning that the “fineness of detail that can be seen is as good as physically possible given the size of the telescope.”
The depth quality of these images is just a taste of what’s to come with JWST. Each image is like its own “Deep Field,” – showing innumerable stars and galaxies – like the famous Hubble Deep Field images, but even deeper.
“These images have profoundly changed the way I see the universe,” said Scott Acton, Webb wavefront sensing and controls scientist at Ball Aerospace. “We are surrounded by a symphony of creation; there are galaxies everywhere! It is my hope that everyone in the world can see them.”
As in the image below, which shows even more detail of the observations, the sharpness and clarity remains even when you zoom in. NASA explains the images:
Engineering images of sharply focused stars in the field of view of each instrument demonstrate that the telescope is fully aligned and in focus. For this test, Webb pointed at part of the Large Magellanic Cloud, a small satellite galaxy of the Milky Way, providing a dense field of hundreds of thousands of stars across all the observatory’s sensors. The sizes and positions of the images shown here depict the relative arrangement of each of Webb’s instruments in the telescope’s focal plane, each pointing at a slightly offset part of the sky relative to one another. Webb’s three imaging instruments are NIRCam (images shown here at a wavelength of 2 microns), NIRISS (image shown here at 1.5 microns), and MIRI (shown at 7.7 microns, a longer wavelength revealing emission from interstellar clouds as well as starlight). NIRSpec is a spectrograph rather than imager but can take images, such as the 1.1 micron image shown here, for calibrations and target acquisition. The dark regions visible in parts of the NIRSpec data are due to structures of its microshutter array, which has several hundred thousand controllable shutters that can be opened or shut to select which light is sent into the spectrograph. Lastly, Webb’s Fine Guidance Sensor tracks guide stars to point the observatory accurately and precisely; its two sensors are not generally used for scientific imaging but can take calibration images such as those shown here. This image data is used not just to assess image sharpness but also to precisely measure and calibrate subtle image distortions and alignments between sensors as part of Webb’s overall instrument calibration process. Credit: NASA/STScI
While the mirror is now fully in focus, engineers will still need to make small periodic adjustments to the mirror segments during the lifetime of the mission. Even small changes in temperature or movements of the spacecraft can alter the alignment.
“Our plan is check the alignment every two weeks,” Feinberg told me earlier this year. “But we will take data roughly every two days, and look at it. So, we have the ability to do it even more frequently, but it may be that we’ll find we don’t need to do it every 2 weeks. This is one of the things we are interested to learn — is how frequently we’ll have to update the mirror.”
You can keep track of JWST’s instrument commissioning phase at the Where’s Webb site.