American Scientist

For months, the team in charge of the James Webb Space Telescope (JWST) maintained spy-level secrecy around the first targets that would be surveyed by the giant observatory. The suspense started building at the telescope’s flawless launch on Christmas Day, 2021, and escalated sharply with the start of full operations this summer. Now, the first images are out, and they were worth the wait.

JWST can’t help but make notable discoveries everywhere it looks, because its capabilities go far beyond those of any of its predecessors. Its 6.5-meter-wide mirror, composed of 18 gold-coated beryllium hexagons, collects more than six times as much light as the Hubble Space Telescope. Its detectors can observe infrared rays out to a wavelength of 30 microns, allowing it to peer through dust and to view the stretched, reddened light from the early universe. Other space telescopes have focused on the infrared sky, but not with anything like JWST’s sensitivity.

In July, NASA and the European Space Agency released five public images that provide a first demonstration of those capabilities in action. “We saw that the telescope is working perfectly, but we knew that,” says John Mather, an astrophysicist at NASA’s Goddard Space Flight Center and senior project scientist for JWST. “What we didn’t know was, what does the universe look like?”

One of the images is a panorama of NGC 3324 (above), a star-forming region, located 7,600 light-years away within a larger structure called the Carina Nebula. The mountains of clouds in the lower part of the image (colored orange, indicating longer infrared wavelengths) are thick clumps of hydrogen, molecular gas, and dust. Gravity is pulling that material together, collapsing it into infant stars that dot the clouds. The upper part of the image (blue, denoting shorter wavelengths) looks relatively clear because intense radiation from more fully developed stars has burned away the dust. The scene is about 16 light-years wide.

The dramatic, hard-edged boundary between the “mountains” and “sky” in the JWST image indicates that we are looking at the nebula edge-on, seeing a cross section through time: The mature stars in the upper section of NGC 3324 are a few million years older than the ones below. Many of the details in the lower region—especially the heavily obscured initial stages of star formation—were invisible in Hubble images of the same region (above, inset) and thus have never been seen clearly before. Mather is struck by all the jets and streamers, which trace the complex ways gravity and magnetism sculpt new stars and planets. “There’s one thing that looks like a tube that comes up, bends over, and goes down again,” he says. “I don’t know what that is.”

Another of the early-release JWST images showcases the other end of stellar evolution. The Southern Ring Nebula (formally NGC 3132, below, left) is a luminous bubble blown out over several millennia by a dying star some 2,500 light-years from us. When a midsize star like the Sun begins to use up its nuclear fuel, it swells into a red giant and then turns unstable, shedding its outer layers. That shedding is what we see here, with multiple shells and swirls indicating that the star blew out material in a sequence of convulsions.

Further complicating the picture, a long-wavelength version of the JWST image (above, right) clearly shows not one but two stars at the center. The brighter one, on the right, is a stable star at an earlier stage of evolution; its radiation helps light up the nebula, while the orbital movements of the two stars around each other stir the pot with turbulent motions. The dimmer, dying star is almost invisible at shorter wavelengths, implying that it is surrounded by a cocoon of dust—perhaps another shell being added to the ring. “A lot of the fine structure here is caused by dust, including polycyclic aromatic hydrocarbons—complicated hydrocarbon molecules like you find in household solvents or diesel fumes,” Mather says. These molecules could eventually seed the next generation of stars and planets with the carbon compounds needed for life.

All of this is just the beginning. Other JWST observations are uncovering evidence of the long-sought infant galaxies in the early universe, analyzing the chemistry of planets around other stars, and tracing disks of gas around supermassive black holes. “The telescope’s optical performance is even better than we required it to be,” Mather says; it shows details as small as 40 milliarcseconds, close to the theoretical optical limit.

JWST’s exquisite performance already has Mather itching to do even better: “It tells us that the next generation of telescopes we’re supposed to build is possible.”

A podcast interview with John Mather.