Why the new James Webb Space Telescope images are such a big deal

The JWST can simply see more of the universe than the Hubble Space Telescope could.

Last year, before the launch of the James Webb Space Telescope, I wrote: “the largest space telescope in history is about to blow our minds.”

Consider this mind blown. NASA has finally revealed its first images from the space-based observatory. These images are decades in the making, and come after years of delays and budgets being blown. But they do not disappoint. Consider this very first image released by the space agency on Monday:

What makes this image so mind-blowing is how small it is, and how large it is, at the same time.

It’s small in the sense that this image represents only a teensy tiny portion of the night sky. Imagine you are holding out a grain of sand at arm’s length. The area of sky that grain covers — that’s the size of the area captured in the above image.

But it’s huge in the sense that nearly every object in this image is a galaxy (besides the bright spiky starbursts, which are stars in the foreground). Think about that: In every pinprick of sky, there are thousands and thousands of galaxies, at least.

And while it appears to us as a flat image, this image reveals the depths of the universe, and is a window through time. The very faintest, smallest blips of light in this photos are images of galaxies as they existed more than 13 billion years ago, near the very beginning of time (that light has been traveling through space ever since). And not only can Webb capture images of galaxies this old; the space telescope can make measurements about what elements those early galaxies are composed of.

An image like this is akin to a core sample of a sedimentary rock. It shows the evolution of the universe over time in its many layers.

And it represents a huge improvement over the capabilities of the Hubble Space Telescope, which, until the launch of the Webb, was the largest observatory in space. Hubble’s mirror is an impressive 7.8 feet in diameter. Webb’s beautiful, gold-hued mirrors combine for a diameter of 21.3 feet. Overall, that amounts to more than six times the light-collecting area, and when it comes to telescopes, more light collecting equals more detail.

You can see the improvements Webb brings over the Hubble already. The Hubble Space Telescope previously made similar observations of the same galaxy cluster Webb captured above.

In the below image slider, the Hubble view is on the left. On the right, Webb’s view is more detailed. More of the fainter galaxies in the background are more easily distinguished. You can also more easily see how some galaxies are warped more clearly, the result of their light passing through gravitational lenses of the galaxies that are closer in the foreground. (To note: these images aren’t perfectly aligned, but you’ll still be able to see the stark difference in detail).

The Webb’s other advantage over Hubble is the type of light it collects.

Light comes in a lot of different varieties. The human eye can see only a narrow band known as visible light, but the universe contains lots and lots of light outside this range, including the higher-frequency, higher-energy forms: ultraviolet light and gamma rays. Then there’s the lower-energy light with longer wavelengths: infrared, microwaves, radio.

The Hubble Space Telescope collects visible light, ultraviolet, and a little bit of infrared. The Webb is primarily an infrared telescope, so it sees light that’s in a longer wavelength than our eyes can see. This seems nerdy and technical, but it’s actually what allows Webb to look further back in time than the Hubble.

Infrared light is often very old light, due to a phenomenon called redshifting. When a light source is moving away from a viewer, it gets stretched out, morphing into a longer and longer wavelength, growing redder. It’s similar to what happens to the sound when a siren goes by: The pitch increases as the siren approaches, then decreases as it trails away. Because space is constantly expanding, the farthest things away from us in the universe are moving away from us, their light growing redder and redder before eventually dropping into the infrared spectrum. Infrared is invisible to human eyes, but Webb can capture it in stellar detail.

NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)

On Tuesday, NASA released even more images from Webb, showing off its impressive capabilities. Here, see the Carina Nebula, an area of star formation. Infrared light is less obscured by cosmic dust, and so the Webb telescope can reveal more stars in this region than Hubble could. “Webb reveals emerging stellar nurseries and individual stars that are completely hidden in visible-light pictures,” NASA explains.

Here, Webb spots a quintet of galaxies. “Webb shows never-before-seen details in this galaxy group,” NASA relays. “Sparkling clusters of millions of young stars and starburst regions of fresh star birth grace the image.”

In another stunning image, Webb observes the remains of a dying star in the Southern Ring Nebula. On the left below, the nebula is captured in near-infrared, and on the right, it is captured in mid-infrared, which each bring out different details in this cataclysm. The dim star in the center has been “sending out rings of gas and dust for thousands of years in all directions,” NASA writes.

This is just the beginning of the Webb’s scientific mission. In the future, scientists hope to use it to see the very first galaxies, which held the very first stars, and understand a time period called “cosmic dawn,” when the universe became transparent to starlight for the first time.

Before cosmic dawn, the universe was shrouded by a “dense, obscuring fog of primordial gas,” as the National Science Foundation explains. There’s no light that reaches our telescopes from this time, which is called the cosmic dark ages. (There is some background radiation from the Big Bang called the cosmic microwave background, a faint glow that shines to us from before the dark ages. But for the most part, the dark ages is a blank spot in our timeline of the universe.)

Astronomers hope the Webb will help them understand the end of the dark ages and figure out what caused this fog to lift, ushering in the cosmic dawn.

Scientists are also excited to use Webb’s infrared capabilities to study exoplanets, which are planets that orbit stars other than our own. Webb is unlikely to see an exoplanet directly, but what it can do is observe the stars they orbit. When a planet orbits in front of the star, the light from the star passes through the planet’s atmosphere like a filter. Scientists can study the quality of light coming from that filter, and determine the composition of the planet’s atmosphere from it. And the team of scientists working on Webb have already done this. On Tuesday, NASA announced Webb detected water in the atmosphere of a gas giant planet orbiting a Sun-like star.

Advances like the James Webb Space Telescope make me think about how we, humanity, are a part of the universe that looks back upon itself. The Big Bang, the birth of stars, the formation of galaxies… we are just as much a consequence of the physics and evolution of the universe as anything else that exists out there. So when we peer back through the cosmos with a telescope like the Webb, we’re completing a loop. We’re building a tool to make the universe, perhaps, a bit more self-aware.

The Webb, at its most basic function, allows us to see more of the universe, and farther back in time. This is just the beginning. There’s so much more to see.

Further reading: Space telescopes

• Webb won’t be the last space telescope. Here’s a look at the potential space telescopes of the future, and what they could teach us.
• More on the technical capabilities of the JWST here.
• Why the new space telescope looks so strange.