JWST is better than anyone expected — here’s why
Humanity's newest, most powerful space telescope is performing even better than predicted. The reason why is unprecedented.
This image features data from 10 different JWST filters: 6 from the near-infrared and 4 from the mid-infrared. As a result, features that include stars, gas, dust, and various molecular signatures can all be revealed at once, showcasing where star formation is occurring and will occur in the future. Molecular gas, present in great abundance, is the key.
Credit: NASA, ESA, CSA, STScI, Webb ERO Production Team
Key Takeaways
- Telescopes of all types have to reckon with noise and imperfections from a variety of sources: thermal noise, stray light, dust, and more.
- Although JWST is located in space, it's not immune to these concerns, but a series of successes have led it to perform better than even the most optimistic astronomers had anticipated.
- The key reason is that JWST and all of its optics and instruments were kept cleaner than in any observatory ever, leading it to almost double the expected performance.
On Christmas Day, 2021, astronomy forever changed with JWST’s launch.
On December 25, 2021, as the solar array deployed 29 minutes after launch, and ~4 minutes ahead of schedule, it became clear that NASA’s James Webb Space Telescope was operational, receiving power, and well on its way toward its ultimate destination. The launch was an unparalleled success.
By mid-2022, a fully calibrated JWST unveiled its first science images.
This almost-perfectly-aligned image composite shows the first JWST deep field’s view of the core of cluster SMACS 0723 and contrasts it with the older Hubble view. The JWST image of galaxy cluster SMACS 0723 is the first full-color, multiwavelength science image taken by the JWST. It was, for a time, the deepest image ever taken of the ultra-distant Universe, with 87 ultra-distant galaxy candidates identified within it. They await spectroscopic follow-up and confirmation to determine how distant they truly are. but even from this first image, JWST observations suggested that the number and density of bright, early galaxies may pose a problem for astronomers.
Its images were sharp, pristine, beautiful, and unprecedentedly informative.
This contrast of Hubble’s view of Stephan’s Quintet with JWST’s NIRCam view reveals a series of features that are barely apparent or not obvious at all with a shorter set of more restrictive wavelengths. The differences between the images highlight what features JWST can reveal that Hubble misses.
But in some sense, they were almost too good.
This animation showcases JWST’s unique near-infrared views of Jupiter. In addition to the bands, the great red spot, and the “atmospheric haze” visible at the day/night boundary of Jupiter, a number of moon, ring, and auroral features are seen and labeled. A single NIRCam or MIRI frame is just barely large enough to hold all of Jupiter’s disk within it, enabling spectacular views of this world with JWST. With an expected lifetime to last until the mid-2040s, JWST will observe multiple Jovian solstices and equinoxes, but won’t last until Uranus reaches its equinox phase.
JWST’s views were sharper, with less noise, than anyone had predicted.
This three-panel animation shows three different views of the center of the Phantom Galaxy, M74 (NGC 628). The familiar color image is the Hubble (optical) view, the second panel showcases near-infrared views from both Hubble and Webb, while the mid-infrared panel shows the warm dust that will eventually form new stars at a later time, containing data from JWST alone.
The key was understanding why, so this unprecedented success could be repeated.
This three-panel animation shows the difference between 18 unaligned individual images, those same images after each segment had been better configured, and then the final image where the individual images from all 18 of the JWST’s mirrors had been stacked and co-added together. The pattern made by that star, a “snowflake” unique to JWST, can only slightly be improved upon with better calibration.
Although JWST displays many remarkable improvements, one advance was critical.
JWST’s diffraction spikes, seen in great detail around the star 2MASS J17554042+6551277, are the same spikes seen in the first successful alignment image. The science data, as evidenced by the glorious detail of background galaxies, has helped revolutionize what we know about the Universe in, thus far, under one full year of science operations.
Sure, the instruments are astoundingly good, with near-perfect photon efficiency.
The cryocooler for the Mid-Infrared Instrument (MIRI), as it was tested and inspected back in 2016. This cooler is essential for keeping the MIRI instrument at about ~7 K: the coldest part of the James Webb Space Telescope. If it gets warmer, the longest wavelengths will return nothing but noise, as the telescope will actually see itself radiating at higher temperatures. Performance so far indicates no discernible noise, indicating the instrument team has done a tremendous job.
The pointing and guiding system, as well as signal throughput, are performing optimally.
The Fine-Gudance Sensor aboard the JWST will track guide stars to point the observatory precisely and accurately and will take calibration images rather than images used to extract scientific data. It is currently performing even better than its design specifications would indicate.
The telescope is kept sufficiently cold; thermal emission and instrument noise are negligible.
Group photo of James Webb Space Telescope project members with the complete Integrated Science Instrument Module (ISIM). The four instruments included inside the ISIM include the Near-Infrared Camera, the Near-Infrared Spectrograph, the Mid-Infrared Instrument, and the Fine Guidance Sensor/Near Infrared Imager and Slitless Spectrograph.
Additionally, the optics are so good that stray light — normally problematic — is negligible.
This small-seeming image is a scaled down version of the full ~140 megapixel field-of-view comprehensively examined after JWST had been fully aligned and calibrated. The bright star at the lower-left of the photo is the famed “alignment star” from JWST’s first aligned image. There is practically no stray light detectable at all.
But JWST’s biggest advance is in controlling its PSF: point spread function.
This simulation of spherical aberration shows how a point source is seen by a perfectly spherical aperture if the object is overfocused (left), underfocused (right), or perfectly focused (center), along with being properly corrected for wavelength (middle row) versus being either slightly overcorrected (top row) or undercorrected (bottom row). The extreme lower-right image shows the original spherical aberration in Hubble’s original WFPC camera. Hubble’s primary mirror had problems with spherical aberration; JWST’s mirrors do not.
JWST focuses its light better than any space-based or ground-based telescope ever.
Shown during an inspection in the clean room in Greenbelt, Maryland in late 2021, NASA’s James Webb Space Telescope was photographed at the moment of completion. Only weeks later, it would successfully launch and deploy, leading to an unprecedented set of advances in astronomy. From mirrors to instruments, it was kept cleaner, from start to finish, than any observatory ever.
Why? Because — from mirrors to instruments — it was kept cleaner than any observatory ever.
NASA’s James Webb Space Telescope, as shown during a “lights out” inspection after its final vibration and acoustic test, performed in October of 2020. Having passed that final test without any red or yellow flags, Webb was deemed ready for launch, and after about 6 months of deployment and calibration, began taking science data.
Advances in clean-room technology and handling enabled a PSF twice as sharp as required.
The stellar streams being ripped from one of the interacting member galaxies of Stephan’s Quintet glitters in this image, while background galaxies shine from much farther away. The new stars that form may not remain gravitationally bound and undisturbed for long, but while they persist, will form collections of stars (or galaxies) that have no dark matter within them at all.
As a result, JWST science is more informative than anyone expected.
This image, a portion of a wide-field view of Neptune taken with JWST’s NIRCam imager, showcases Neptune, its giant moon Triton, faint features on and around Neptune, including its rings and smaller moons, and a smattering of background galaxies and stars from within the Milky Way.
With the fuel saved from a near-perfect launch, JWST should remain operating so pristinely through 2044.
Overlaid with (older) Hubble data, the JWST NIRCam image of the Southern Ring Nebula is clearly superior in a variety of ways: resolution, the details revealed, the extent of the outer gas, etc. It truly is a spectacular reveal of how stars like the Sun end their lives.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.
