Astronomers had expected extraordinary science from NASA’s new James Webb Space Telescope. But when the first set of pictures and data was released in July, they were stunned.

NASA/MSFC/David Higginbotham; NASA, ESA, CSA, STScI

“The first images are spectacular!” gushes Neta Bahcall, the Eugene Higgins Professor of Astrophysics at Princeton, who for eight years served on an advisory committee for the telescope, called JWST or simply Webb. “Even better than we expected.”

Princeton astrophysicist Jenny Greene is similarly ecstatic. “Wow!” she says of squiggles showing the breakdown of colors from a far-away galaxy. The colors, or spectra, tell of elements and molecules there. She was “so inspired” by the telescope’s power that she is about to submit a paper presenting a method to find seed black holes — black holes at the initial stage — in the data. “We are very excited,” she says.


Astronomers expect a gold rush of discovery in the coming years as the telescope peers around the universe — at the earliest stars and galaxies, at planets around other stars, at stellar nurseries and dead stars within our own galaxy. “We have yet to observe the era of our universe’s history when galaxies began to form,” NASA explains on its website. “We have a lot to learn about how galaxies got supermassive black holes in their centers. … We don’t know how many planetary systems might be hospitable to life, but Webb could tell whether some Earth-like planets have enough water to have oceans.” 

“There’s nothing comparable to Webb,” says Adam Burrows ’75, a Princeton astrophysics professor who serves on the Space Studies Board of the National Research Council, which reviews U.S. space-science research.

Not long ago — last year, really — the mood around the telescope was more somber. After a decade of delays, management and technical blunders, and a price tag that had risen to $10 billion, news articles matter-of-factly described it as “beleaguered.” JWST seemed to be the telescope that would never launch.

Then, on Christmas Day last year, it was finally ready for liftoff. For astronomers at Princeton and throughout the world, this was a moment of anticipation and high anxiety, their careers hanging in the balance.

The nervous Christmas Day watchers, huddled around television and computer screens, included Tea Temim, a research astronomer who joined Princeton last year but previously worked at the Space Telescope Science Institute in Baltimore, which is in charge of operating JWST. She watched the launch online at home with her toddler son while wearing an N95 mask; except for the little boy, the entire family had contracted COVID. 

“Maybe the Omicron aspect was a good distraction,” she says. “I don’t remember when I’ve been that nervous. I basically had a knot in my stomach for the week ahead of the launch.”

Robel Geda, now a second-year Princeton graduate student, returned to the space telescope institute to watch with former colleagues. He had been a computer engineer there, writing software and visualization tools that will help astronomers glean slivers of knowledge out of a tsunami of JWST data. 

If the rocket had exploded, if some flaw had slipped past the many tests, if JWST had failed, then all the projects that astronomers had spent years planning to use it for would have been for naught. “We would have recovered from it over time,” Bahcall says, “but it would have been very damaging.”

On Christmas morning, the telescope roared to space on top of an Ariane 5 rocket from French Guiana and uneventfully went on its way, headed on a trajectory to its destination nearly a million miles from Earth.

As Geda watched in Baltimore, he felt nervous and excited at the same time. “It was a big relief once it was detached from the rocket,” he says. “It was like a home run. It was one of the best days of my life, I have to say.”

The telescope that had seemed so snake-bitten on the ground has so far performed flawlessly in space. Perhaps the rockiest part of the mission so far has to do with its name: James Webb, NASA’s second administrator, was second-in-command at the state department in the Truman administration during the Lavender Scare, when thousands of federal employees lost their jobs because they were gay or lesbian; as a result, many astronomers wanted the telescope to be renamed and refer to it by its initials only. In any case, over the course of a month, the telescope, neatly packed up for launch, deployed the 18 large, gold-plated, hexagonal pieces of the mirror, and a sunshield to keep itself cool unfolded into place without snags.

Everything that could have gone wrong did not go wrong.

Princeton research astronomer Tea Temim will use data from the Webb telescope to study the Crab Nebula, remnants of an exploded star 6,500 light-years from Earth.
Sameer A. Khan h’21

In July, President Joe Biden took the opportunity to bask in the astronomical success, showing off Webb’s first full-color image: a patch of sky filled with stars and galaxies. Other early observations included a nursery of newborn stars, a billowing bubble of gases from a dying star, and the atmosphere of a hot, steamy, alien planet.

Almost since the Hubble Space Telescope launched in 1990, astronomers have dreamed of a bigger space telescope that would follow it. Hubble, still in operation today, proved the worth of putting a telescope in space — an idea that Lyman Spitzer *38, the late, renowned Princeton astrophysicist, championed in the late 1940s, a decade before the first artificial satellite, Sputnik, was launched. 

Hubble’s mirror, almost 8 feet wide, is far smaller than large ground-based telescopes, but unlike those telescopes, it can peer out without any of Earth’s atmosphere blocking and distorting the light arriving from distant stars.

Astronomers hope that Webb, with a larger mirror — more than 21 feet in diameter — can see even more distant stars. Because of the constant speed of light, looking farther into the cosmos is also looking back in time, to within a few hundred million years after the Big Bang. The hope is to see some of the earliest galaxies.

“What did they look like?” Bahcall asks. “How did they form? What type of stars they contain? And how have they been evolving, all the way from the very early days of the universe, from the baby universe to today?” This is the missing chapter in our knowledge of the universe. It was the supernova explosions of the first stars that filled the universe with the elements that could form planets like Earth and beings like us. 

More distant objects are dimmer, but they are also redder. Because of the expansion of the universe, the most distant stars and galaxies are moving away faster. That stretches out the wavelength of the photons, much as the siren of a police car moving away sounds lower in pitch. The lengthened wavelengths fall out of the spectrum of visible light into what is known as the infrared. Infrared light is readily absorbed by water vapor, so it’s not easily observed by telescopes on the ground.

Webb is much farther away than Hubble, which orbits 350 miles above Earth. The new telescope is more than four times the distance from the Earth to the moon, at a location known as L2, or the second Lagrange Point. There, the gravitational pull of the Earth and sun balances the outward centrifugal acceleration of a circular orbit, and the remote location makes it easy to keep the telescope pointed away from the sun, with a shield to maintain super-cold temperatures needed for undistorted infrared observations.

This JWST image of the Cartwheel Galaxy was released by NASA in August. The galaxy, about 500 million light-years away, resulted from the high-speed collision between a large spiral galaxy and a smaller galaxy.
NASA, ESA, CSA, STScI, Webb ERO Production Team

Rachel Bezanson, who was a postdoctoral researcher at Princeton during the 2016-17 academic year and is now an assistant professor at the University of Pittsburgh, is co-principal investigator of a project known as UNCOVER that will be conducted during JWST’s first year of operation.

“I started thinking about it back when I was a postdoc at Princeton,” she says. Bezanson and her colleagues, who include Princeton astrophysicist Jenny Greene, will point the telescope at a massive cluster of galaxies known as Abell 2744, or Pandora’s Cluster. The cluster is just 4 billion or so light-years away — which on the scale of the universe is relatively close — and the telescope will stare and take pictures in that direction for 30 hours. The interest is not so much in Pandora’s Cluster but in using it to take advantage of Albert Einstein’s theory of general relativity — that mass curves space, and lots of mass curves space a lot. The cluster will thus be a magnifying glass to brighten distant, dim galaxies behind it.

Astronomers have employed the same technique with Hubble, but Hubble’s smaller mirror collects less light, and its instruments are mostly tuned to shorter visible and ultraviolet wavelengths, not the infrared.

That’s the first part of the project. “We’re going to use those images to find the coolest, craziest objects that we can,” Bezanson says. Then, about eight months after the initial observations, the astronomers will have 20 more hours of telescope time to take detailed measurements of about 500 of those coolest, craziest objects, breaking down the light to a set of colors. 

“That’s using a slightly different instrument,” Bezanson says, “to basically create spectra — create rainbows — from the objects.” The breakdown of infrared colors will help pin down the distances as well as identify some of the ingredients in those objects. The hope is that the discoveries will include some of the first stars to light up the universe. Those early stars are expected to be different from the ones shining today because the universe contained hydrogen and helium and a smidgen of lithium. It was devoid of all heavier elements.

“It’s kind of inevitable that we will see the light from those stars,” Bezanson says. 

In addition to collaborating with Bezanson, Greene is a member of two other JWST observing teams that will examine galaxies not so far away — in particular, studying the gargantuan black holes found at the center of most large galaxies. Black holes are the maws of inescapable gravity so strong that not even light can escape and space-time seems to collapse on itself.

Just outside black holes, the mayhem of material falling into the gravitational abyss creates jets of particles and radiation that are incredibly bright. In 2019, astronomers using a network of radio telescopes around the world created an image of the supermassive black hole inside the galaxy Messier 87, about 55 million light-years away. Dust obscures the visible wavelengths of light, preventing scientists from seeing much detail, but infrared light passes unimpeded. “Being in the infrared really allows us to pierce through the dust and ask new questions about how black holes are interacting with their surroundings,” Greene says. 

A question has nagged Greene for her entire career: How did the supermassive black holes at the center of galaxies form? Were they star-size black holes that fell into each other, or did the gigantic black holes form out of the collapse of a gigantic gas cloud? “What are their seeds?” she asks. 

If those galactic black holes formed directly from the gas clouds, “we should be able to see them forming,” she says.

Graduate student Robel Geda worked as a computer engineer who wrote software meant to help astronomers make effective use of the telescope data.
Sameer A. Khan h’21

Temim is involved with 12 JWST observing programs, including one where she is the principal investigator. In that one, she will study the Crab Nebula — wispy remnants, 6,500 light-years from Earth in our Milky Way galaxy, of an exploded star. Sky-watchers in China and elsewhere would have seen that explosion, or supernova, on July 4, 1054, and it was so bright that it could be seen even during the day for more than three weeks.

Even though the Crab Nebula is one of the most studied objects in astronomy, mysteries remain. One of them: How was the supernova that bright? The composition of the glowing remnants suggests that the star that exploded was fairly small, with a mass about nine times that of the sun. Perhaps that star had shed gas before its demise and the shock wave caused that to light up as well.

With the new telescope, astronomers will have a clearer look at the infrared emissions from the nebula. The JWST images could also give new clues about the dying star and how it exploded. “The picture isn’t quite clear,” Temim says.

The Crab Nebula data could help with another unsolved question: Why is the universe dusty? It’s known that supernovas throw out particles that are like fine sand grains or smaller, but so far, the Crab Nebula does not seem to be all that dusty. “We just don’t see as much as expected,” says Temim.

Temim hopes that the higher-resolution images from JWST will be able to tease apart infrared emissions emanating from dust from those emissions coming from gasses. That would then provide a detailed map of dust in the nebula.

One of the images released in July was of the Southern Ring Nebula, another colorful bubble surrounding a dying star. The star at the center of that nebula was not massive enough to collapse in a supernova explosion. Still, it offers a hint of what JWST will reveal for Temim’s research.

“As this gas expands away from the star and cools, dust condenses and is now emitting in the infrared, similar to how the dust formed in the supernova ejected material in the Crab,” Temim says. “The Southern Ring nebula gives us a preview of the detail that we will be able to observe in the Crab. Temim’s other telescope projects include observations of another supernova remnant, Cassiopeia A, and a supernova that exploded in 1987.

A universe of other questions could be answered, too. 

Brianna Lacy *21, now a postdoctoral researcher at the University of Texas at Austin, is developing models to help researchers interpret JWST observations. She’s interested in planets that have not been seen directly but were discovered when a star dimmed slightly as a planet passed in front, blocking part of the starlight. 

Part of the starlight also passes through the atmosphere of the planet, causing a subtle shift in colors. JWST’s infrared acuity could show what molecules are floating in the atmosphere, and some of those molecules, like oxygen, could offer tantalizing hints of life on those planets. The same technique has been used for Hubble observations, but with JWST’s larger mirror, astronomers will be able to study smaller planets closer to a star — “even reaching down to habitable distances,” Lacy says. 

That is, scientists will be able to peer into the atmospheres of rocky planets somewhat bigger than Earth orbiting in a region where they could possess temperate conditions favorable for life.

And Webb’s data could tell Burrows if his theories about such supernova explosions are right or not. He wants to understand the turbulence within an exploding star by looking at what is left today, including the heavier elements that were created, the shock wave emanating outward, and the neutron star husk that remains of the dead star. “We want to be able to work backwards to the fundamental phenomenon that happens in the first seconds of the explosion,” he says. The topic represents “a half-century journey of great complexity,” he wrote in a recent paper. 

“[The telescope’s] capabilities — if it realizes those capabilities — will really be an eye-opener for us,” Burrows says. Astronomers, he says, will gain “understanding of the universe in ways that we probably can’t completely understand or contemplate now.” 

Kenneth Chang ’87 is a science reporter for The New York Times. 

About the ‘Spin’ on Our Cover

The image on this month’s cover — of NGC 3324, a star-forming region in the Carina Nebula — is the same one that graced the pages and broadcasts of news outlets around the world in July, when NASA released the first photos taken by the James Webb Space Telescope. But it probably looks a little different to you. That’s because we rotated it 90 degrees, admittedly to better fit PAW’s dimensions, but also to challenge our view of the universe. 

Michael Strauss, chair of astrophysical sciences at Princeton, explains that “there is no ‘up’ in space.” To put it another way, imagine that you stood in the middle of an open field and pointed your camera at the sky. The resulting picture wouldn’t have an identifiable top or bottom. The universe is directionless.

The visual style NASA tends to use for images of space present “solid-seeming surfaces at the bottom of the frame, vaguely geologic structures rising up, and then empty horizons above,” according to The New York Times, but Strauss confirms the choice is purely aesthetic.