Two Weeks In, the Webb Space Telescope Is Reshaping Astronomy


As soon as President Biden unveiled the first image from the James Webb Space Telescope (JWST) on July 11, Massimo Pascale and his team sprang into action.

Coordinating over Slack, Pascale, an astrophysicist at the University of California, Berkeley, and 14 collaborators divvied up tasks. The image showed thousands of galaxies in a pinprick-size portion of the sky, some magnified as their light bent around a central cluster of galaxies. The team set to work scrutinizing the image, hoping to publish the very first JWST science paper. “We worked nonstop,” said Pascale. “It was like an escape room.”

Three days later, just minutes before the daily deadline on, the server where scientists can upload early versions of papers, the team submitted their research. They missed out on being first by 13 seconds, “which was pretty funny,” said Pascale.

The victors, Guillaume Mahler at Durham University in the United Kingdom and colleagues, analyzed that same first JWST image. “There was just a sheer pleasure of being able to take this amazing data and publish it,” Mahler said. “If we can do it fast, why should we wait?”

The “healthy competition,” as Mahler calls it, highlights the enormous volume of science that is already coming from JWST, days after scientists started receiving data from the long-awaited, infrared-sensing mega-telescope.

The Dawn of Time

One of JWST’s much-touted abilities is the power to look back in time to the early universe and see some of the first galaxies and stars. Already, the telescope — which launched on Christmas Day 2021 and now sits 1.5 million kilometers from Earth — has spotted the most distant, earliest galaxy known.

Two teams found the galaxy when they separately analyzed JWST observations for the GLASS survey, one of more than 200 science programs scheduled for the telescope’s first year in space. Both teams, one led by Rohan Naidu at the Harvard-Smithsonian Center for Astrophysics in Massachusetts and the other by Marco Castellano at the Astronomical Observatory of Rome, identified two especially remote galaxies in the data: one so far away that JWST detects the light it emitted 400 million years after the Big Bang (a tie with the oldest galaxy ever seen by the Hubble Space Telescope), and the other, dubbed GLASS-z13, seen as it appeared 300 million years after the Big Bang. “It would be the most distant galaxy ever found,” said Castellano.

Both galaxies look extremely small, perhaps 100 times smaller than the Milky Way, yet they show surprising rates of star formation and already contain 1 billion times the mass of our sun — more than expected for galaxies this young. One of the young galaxies even shows evidence of a disklike structure. More studies will be done to break apart their light to glean their characteristics.

Another early-universe program has also turned up “incredibly distant galaxies,” said Rebecca Larson, an astronomer at the University of Texas, Austin and a member of the Cosmic Evolution Early Release Science (CEERS) survey. Just weeks into the survey, the team has bagged a handful of galaxies from the universe’s first 500 million years, although Larson and her colleagues haven’t released their exact findings yet. “It’s better than I imagined and it’s only the beginning,” she said.

More early galaxies hide in the image of the galaxy cluster presented by President Biden and studied by Pascale and Mahler. Called SMACS 0723, the cluster is so heavy that it bends the light of more distant objects, bringing them into view. Pascale and Mahler found up to 16 remote galaxies that have been magnified in the image; their exact ages aren’t yet known.

The telescope took a closer look at one distant galaxy in the image, a smudge of light that dates to 700 million years after the Big Bang. With its spectrograph, JWST detected heavy elements, particularly oxygen, in the galaxy. Now scientists are hoping the telescope will find an absence of heavy elements in even earlier galaxies — evidence that these galaxies contain only Population III stars, the hypothesized first stars in the universe, thought to have been monstrously huge and made entirely from hydrogen and helium. (Only as those stars exploded did they forge heavier elements such as oxygen and spew them into the cosmos.)

“We’re looking for galaxies where we see no heavy elements,” said Andy Bunker, an astrophysicist at the University of Oxford. “That might be a smoking gun for the first generation of stars formed from primordial hydrogen and helium. Theoretically they should exist. It depends whether they’re bright enough.”

Galactic Structure

For scientists seeking to understand the structure of galaxies and how stars form within them, JWST has already provided impactful data.

One observing program, led by Janice Lee at the National Science Foundation’s NOIRLab in Arizona, looks for young sites of star formation in galaxies. On behalf of Lee’s team, JWST observed a galaxy 24 million light-years away called NGC 7496, whose young star-forming regions have until now been shrouded in darkness; Hubble’s instruments were unable to penetrate the thick dust and gas that surrounds these regions. JWST, though, can see infrared light that bounces off the dust, allowing the telescope to probe close to the moments when the stars switched on and nuclear fusion ignited in their cores. “The dust is actually lighting up,” said Lee.

What’s most remarkable, she said, is that NGC 7496 is a normal galaxy, “not a poster-child galaxy.” Yet under the watchful eye of JWST, it suddenly comes to life and reveals channels where stars are forming. “It’s just phenomenal,” she said.

John Barentine, an astronomer at the dark-sky conservation firm Dark Sky Consulting in Arizona, meanwhile, made a more serendipitous discovery in one of JWST’s first images. The telescope’s picture of the Southern Ring Nebula, 2,500 light-years from Earth, showed remarkable clarity. Off to the side, an intriguing galaxy viewed edge-on (a unique vantage point for studying the galaxy’s central bulge), previously misidentified as part of the nebula itself, poked into view.

“We have this exquisitely sensitive machine that is going to serendipitously reveal things we didn’t even know we were looking for,” Barentine said. “In almost every image Webb takes, it’s worth poking around in the background.”

An Eye on Stars and Planets

Smaller targets are in JWST’s crosshairs, too, including the planets of our own solar system. Jupiter appeared in magnificent fashion as part of the first batch of images, captured in an exposure lasting just 75 seconds.

Astronomers know that Jupiter’s upper atmosphere is hundreds of degrees hotter than the lower atmosphere, but they aren’t sure why. By detecting infrared light, JWST could see the heated upper atmosphere shining; it appears as a red ring around the planet. “We have this layer a few hundred kilometers above the cloud decks, and it’s glowing because it’s hot,” said Henrik Melin, a planetary scientist at the University of Leicester. “We’ve never seen it like this before on a global scale. That’s an extraordinary thing to see.”

Melin’s program plans to use JWST in the coming weeks to study the driving force behind this atmospheric heating.

Hiding in JWST’s image of Jupiter is the volcanic moon Io interacting with Jupiter’s aurora — creating a small bump in the aurora. The image reveals “material coming from Io streaming down the magnetic field lines,” said Melin. The effect has been seen before, but it was easily picked out by JWST with barely a glance at the planet.

JWST is probing planets in other star systems too. Already, the telescope has taken a peek at the famous TRAPPIST-1 system, a red dwarf star with seven Earth-size worlds (some potentially habitable), though the data is still being analyzed. Early observations have been released of a less hospitable planet, a “hot Jupiter” called WASP-96 b, in a tight 3.4-day orbit around its star.

JWST found water vapor in the planet’s atmosphere, confirming evidence of water reported days earlier by Chima McGruder of the Harvard-Smithsonian Center and colleagues, who used a ground-based telescope. But JWST can go further; by observing WASP-96 b’s ratio of carbon to oxygen, it may be able to solve a confounding mystery about hot Jupiters: how they attain such close orbits around their stars. More oxygen would suggest that the gas giant initially formed near the star, while a higher carbon ratio would suggest that it formed in more carbon-rich regions further away.

Meanwhile, JWST may have spotted a temporary light in the sky — a short-lived event known as a transient — which it was not initially designed to do. The astronomer Mike Engesser and colleagues at the Space Telescope Science Institute in Baltimore, Maryland (the operations center for JWST), noticed a bright object not apparent in Hubble images of the same region. They think it’s a supernova, or exploding star, some 3 billion light-years away — proof that the telescope can find these events.

JWST should be capable of finding far more distant supernovas too, which will give it another way to serve as a probe of the early universe. It may also find stars being torn apart by the supermassive black holes that reside at galaxies’ centers, something no previous telescope has seen. “For the first time we’re going to be able to peer into these very deep, dark regions,” said Ori Fox, an astronomer at the Space Telescope Science Institute who leads the team studying transients.

Transients, like other astronomical phenomena, are set to be redefined. After decades of planning and construction, JWST has hit the sky running. The issue now is keeping pace with the constant barrage of science coming down from a machine so complex yet faultless it almost defies belief that it was built by human brains. “It’s working, and it’s insane,” said Larson.

Quanta Magazine, 25 July 2022