The first full-color images from the James Webb Telescope are gorgeous, but they’re also full of substantial science.
Webb’s first images revealed the molecular makeup of some of the universe’s oldest galaxies, measured water vapor in an exoplanet’s scorching-hot atmosphere, found the burnt-out stellar core at the heart of a nebula, witnessed a cluster of galaxies merging to form an even larger galaxy, and glimpsed newborn stars never seen by astronomers.
But it wasn’t just about pretty pictures. Each of these pictures has a story to tell us about the machinations of the universe. Some, like a gas giant passing between its star and us, tell us about Earth’s origins. Others tell us about the cycles of star death and rebirth. And a few tell us how the universe may have begun.
Discovering thousands of ancient galaxies
Webb’s first view of the early universe, a dazzling image succinctly called Webb’s First Deep Field, shows thousands of galaxies in an area of space that, if you were looking at it from Earth, would only cover as much sky as a grain of sand held at arm’s length.
Many of the galaxies in the image are recognizable spiral or oval shapes with bright centers, ranging from blue to yellow to orange, and several of them are young enough that they’re still spawning new stars. But thousands more are visible only as tiny reddish specks or streaks in the background — and they’re some of the oldest galaxies we’ve ever seen.
The oldest among them is 13.1 billion years old, dating to less than a billion years after the Big Bang; astronomers know that based on the wavelengths of light Webb measured from that galaxy. And now, astronomers know more about its composition.
Webb’s instruments captured light from the distant galaxy, then split the light into the individual wavelengths that make it up — exactly like shining light through a prism to see a rainbow. Each molecule absorbs and emits light at different wavelengths, so looking at the spectrum of light from an object can reveal what it’s made of.
“We're seeing the elements of oxygen, and hydrogen as well as beyond,” astrophysicist Jane Rigby, a project scientist for the Webb telescope, said during a NASA press event. “This is how the oxygen in our bodies was made, in stars in galaxies, and we're seeing that process get started.”
Although galaxies like this one — and thousands of others in Webb’s Deep Field — are extremely old, they’re also completely new to astronomers, because they are too faint for previous telescopes, like Hubble and Spitzer, to even see.
Because the universe is expanding (for now), distant objects like the galaxies in Webb’s First Deep Field are moving away from us. The Doppler effect stretches out the light waves from these distant, fleeing objects, so they appear further toward the red end of the spectrum. 13.1 billion light years away, and 13.1 billion years in the past, galaxies are moving away from us so fast that their light is stretched into the infrared.
The light from these ancient, distant galaxies is also very faint — partly because they’re so far away and partly because the earliest galaxies in the universe were smaller, dimmer, and cooler than the bigger, brighter galaxies that evolved later.
Images like Webb’s First Deep Field, and the scientific data that come with them, will help astronomers better understand how that evolution happened. But even with Webb’s formidable abilities, the deep field would have been quite a bit shallower without help from a natural telescope: gravitational lensing.
In the foreground of the image, you can see a cluster of bright whitish galaxies called SMACS 0723. Their combined gravity actually bends spacetime around them so that light from objects behind the galaxy cluster gets curved around it as if it were passing through a curved glass lens. That curve distorts the light from those distant objects, which is why you can see smears and curved streaks of light in the deep-field image, but it also magnifies the light, allowing astronomers to see smaller, fainter, and more distant objects.
Finding steam in an alien atmosphere
Some of the most remarkable science in Tuesday’s release isn’t an image — it’s a spectrum (a chart of the different wavelengths of light emitted from an object). It reveals water vapor in the atmosphere of a gas giant orbiting a star 1,100 light years away.
The exoplanet WASP-96b is about the size of Jupiter but only about half Jupiter’s mass. That’s because this distant world orbits so close to its parent star that the star’s heat has actually inflated the planet’s gassy envelope — like a planet-sized, probably-inedible popcorn kernel. (Molecules in a gas tend to get further apart when the gas is heated, so the same amount of exoplanet atmosphere takes up much more room.) WASP-96b is ten times closer to its star than Mercury is to our Sun and zips around a complete orbit in just 3.4 days.
Webb couldn’t see the exoplanet directly, so astronomers watched the star (WASP-96)and measured how its light changed when the exoplanet (WASP-96b) passed between the star and Earth.
“When the planet and its atmosphere passes in front of the star, the starlight filters through the atmosphere,” NASA astrophysicist Knicole Colon said during the event. “You can break that down into wavelengths of light, and you get a bunch of what looks like bumps and wiggles to some people, but it's actually full of information content.”
Telescopes on Earth studied WASP-96b using the same transit method, but in visible wavelengths of light in 2018. Those telescopes found evidence of sodium deep in the lower layers of the gas giant’s atmosphere. Looking at the exoplanet in infrared, Webb’s Near Infrared Spectrometer found the “chemical fingerprint” of water vapor in WASP-96b’s atmosphere.
Webb also found something that changed what we thought we knew about WASP-96b.
“The other thing we can tell actually, is that there's evidence of clouds and hazes,” Colon said. “The water features are not quite as large as we predicted. So we can take that and infer the presence of clouds and hazes.” In 2018, astronomers concluded that the planet’s atmosphere must be clear, because otherwise, the clouds would block light from the sodium in the gas giant’s deeper layers. But according to Webb’s data, WASP-96b is a cloudy world after all.
Peering into the dead heart of a beautiful nebula
Webb revealed the binary star system at the heart of the Southern Ring Nebula, a gorgeous ring of gas and dust expanding outward from the explosive death throes of a star.
“We knew this was a binary star, but we didn’t get to see much of the actual star that produced the nebula,” said Karl Gordon. That star is now a white dwarf, the dense core of what was once a massive star that exploded in a supernova. Most of the star’s mass is now expanding outward at about 14 kilometers per second, forming the ring of the Southern Ring Nebula. What’s left behind radiates heat, also known as infrared radiation, and soft x-rays, but it’s usually lost in the blazing glow of its brighter, still-living companion star. Webb’s Mid Infrared Instrument, or MIRI, changed that.
In the outer shell of the Southern Ring Nebula, where hydrocarbon molecules are forming on dust grains, NIRCam reveals clouds of gas and dust with a spongy texture, riddled with bubbles caused by stellar winds. In MIRI, those clouds appear as a foamy blue network of filaments. Hot, ionized gas in the center of the ring appears as a blue haze in NIRCam’s near-infrared images and bright red in MIRI’s mid-infrared view. And at the heart of it all, two bright stars blaze — one red and one bluish-white.
“In MIRI, the star glows red because it has dust around it,” said Gordon. “We got to see both stars very clearly.”
And NIRCam revealed a hidden “Easter egg” just behind the outer wisps of the dust clouds, near the upper left of the image: an edge-on view of a galaxy. “I made a bet that said no, it's part of the nebula,” admitted Gordon. “Then we looked more carefully at both NIRCam and MIRI images, and it's very clearly an edge-on galaxy, so I lost the bet.”
Watching doomed galaxies crash together
One of Webb’s major science goals is to help astronomers learn more about how the tiny, dim red splotches in the background of Webb’s First Deep Field evolved into large, bright, complex galaxies like our Milky Way. The space telescope’s instruments captured an essential part of that process in action: titanic collisions between merging galaxies.
Between 210 to 340 million light years away, four galaxies are in a slow death spiral. This cluster of galaxies is called Stephan’s Quintet, but one of its members only appears to be part of the group; it’s actually about 200 million light years closer to us than the others. But the other four are slowly crashing into one another, like footage of a train wreck happening in cosmic slow motion.
“They’re locked in a close interaction, a sort of cosmic dance driven by the gravitational force,” said Giovanna Giardino. The two galaxies on the right side of the image are already in the process of merging, and the others will eventually be pulled in as well.
In the near-infrared wavelengths, an arc of bright oranges and reds between the merging pair reveals where shock waves from the collision are rippling through clouds of gas, heating and compressing the gas and triggering waves of star formation.
Meanwhile, in the upper right galaxy, MIRI’s mid-infrared image reveals a monster lurking at the galaxy’s heart: an active supermassive black hole, actively feeding on material from the surrounding galaxy. This active galactic nucleus, as astronomers call it, shows up as a bright glow in the mid-infrared images; in reality, it’s 40 billion times brighter than our Sun.
“We cannot see the black hole itself. But we see the material swirling around being swallowed by cosmic monsters. This gas gets heated to extremely high temperature as it falls into the black hole, and becomes very bright,” said Giordino.
With NIRSpec, the astronomers zoomed in for a closer look at the active galactic nucleus to learn more about what happens while a black hole feasts on its galaxy. “We have this technology that allows us to take 1000s of images of different wavelength channels to understand the composition of the gas, the velocities, and the temperature,” explained Giordino. “That's very important to understand the physics.”
Peeking into a stellar nursery
Amid the mountains of gas and dust that make up the Carina Nebula (home of the Defiant Finger!), Webb’s instruments revealed “hundreds of new stars that we’ve never seen before,” according to NASA astrophysicist Amber Straughn, deputy project scientist for Webb, in one of our galaxy’s most active star-forming regions.
Often, the thick dust clouds of a nebula like Carina can hide the light of newborn stars. But looking in the universe at infrared wavelengths, it’s easier to see through the dust clouds to the stars growing inside. That ability makes Webb the perfect tool for studying the life cycle of stars, starting with stellar nurseries like the Carina Nebula and ending with white dwarfs and growing debris clouds like the Southern Ring Nebula.
The intense stellar winds — blasts of radiation and ionized particles — from those newborn stars carve cavities and bubbles into the gas and dust, giving the nebula its complex, foamy texture in the images. Webb’s high-resolution infrared instruments capture that texture in more detail, which is why the Webb images look so different from Hubble’s wispy, cloudier view of the nebula.
In the process of carving abstract cosmic sculptures in the nebula, those stellar winds help compress and heat the material, triggering more star formation.
“But there's a flip side of this story and also a little bit of a mystery, because these same processes can serve to sort of erode away this material and stop star formation,” said Straughn. “So we have this sort of delicate balance going on of new stars being formed, but at the same time, the star formation is halted.”
That’s the type of mystery Webb’s future observations may help scientists like Straughn better explain.
What’s Next — The next few months of observations will gather data to answer fundamental scientific questions, and they’ve been carefully planned to push the Webb telescope to the limits of its abilities. Those observations will test Webb’s resolution, sensitivity, and ability to track moving targets. And that’s the goal: to figure out precisely what Webb can do and how future astronomers can make the most of the newly-commissioned space telescope.
