If you’re anything like me, you have been sitting in front of your computer and staring with slack-jawed awe at the first images sent by the James Webb Space Telescope (JWST).
They possess a stunningly surface beauty, of course. But I hope you will take a deeper look. A more extended examination reveals details that turn awe into a profound sense of the size and complexity of the universe, of which we are all only tiny components.
This week, let’s take a detailed look at JWST’s first image, a long-exposure photo of the galactic cluster SMACS 0723.
I invite you to use the zoomable version. You can find it at https://webbtelescope.org/news/first-images/gallery/zoomable-image-deep-field-smacs-0723.
First, some background. NASA designed JWST to image the universe in the infrared, the energy band just below red light along the electromagnetic spectrum.
There is a good reason for observing objects in the infrared. Distant galaxies are traveling away from us at nearly the speed of light.
Their doppler shifts redden their light out of the visual and into the longer-wavelength infrared portion of the electromagnetic spectrum. Because of the “redshift,” an image in visible light would show no distant galaxies.
Another problem arises from the gas and dust between us and the most distant galaxies.
The material in intergalactic space is spread out very thinly, less than one atom per cubic meter. However, as astronomer Michael Shull pointed out, “When you add it all up, it’s somewhere between 50 and 80 percent of all the ordinary matter out there.”
Multiply that thin spread of gas and dust over the 13 billion light-years between us and the most distant galaxies, and you have something akin to a brick wall.
You can’t see through a brick wall in visible light. But you can detect the infrared light in the form of heat as it passes through the wall on a summer day.
JWST is a $10 billion heat detector of extraordinary sensitivity. NASA claims that the telescope can “detect the slight heat of a bumblebee at the distance of the moon.”
The patch of sky in the image is no bigger than a grain of sand held at arm’s length. It would look empty in a large visual telescope.
Because JWST has such a sizeable light-gathering mirror, observes in the infrared, and is free of Earth-based atmospheric distortion, it reveals a startling fact about the universe.
There are no empty patches of sky. The universe is teeming with activity everywhere we look.
As Ohio State astronomer Scott Gaudi said in an interview with Live Science, “You … realize there’s no blank sky. There’s something crazy happening everywhere.”
Let’s look at some “crazy” elements of the SMACS 0723 image.
The bright stars you see are in our Milky Way galaxy. The design of the optical system causes their characteristic diffraction spikes.
Galaxies are the basic building blocks of the cosmos. At least six trillion galaxies inhabit the universe.
Every indistinct blotch or arc of light in the image is a galaxy, “thousands upon thousands” of them, as commentators are phrasing it. (It’s too soon to have an exact count.)
Every fuzzy dot you see contains billions of stars, even hundreds of billions.
Now use the zoom function of the image. You will see fine examples of the categories of galaxies — from egg-shaped ellipticals to whirlpool-shaped spirals.
Seen from the top, a spiral galaxy resembles a child’s pinwheel. Seen from the side, it looks like a toothpick with a bulge at its center. You’ll find plenty of them and every category of tilt in between.
A similar image taken by the Hubble Space Telescope, the Ultra-Deep Field, contains about 10,000 galaxies. The Hubble image is a composite of 800 images taken over almost 277 hours of exposure time.
By comparison, the JWST image is a knockoff with an exposure time of only 12.5 hours. There’s no telling how many galaxies JWST will see when astronomers image such patches of sky for more extended periods.
As big as they are, galaxies are not the most extensive structures in the cosmos. That honor belongs to galactic clusters, gravitationally bound collections of galaxies traveling together through space.
SMACS 0723, the foreground galactic cluster, is visible as the brighter, white galaxies near the center of the field.
SMACS 0723 is 4.6 billion light-years away. We see it the way it looked 4.6 billion years ago.
Since one light year is equivalent to 5.9 trillion miles, SMACS 0723 is no slouch in the distance department. However, the universe is 13.8 billion years old. The cluster is close compared to many other galaxies in the field of view.
Such great distances are difficult to put into perspective, but let’s try. When the light from SMACS 0723 began its long 4.6-million-light-year journey toward Earth, there was no Earth to which it could travel. Our planet began to form about 4.54 billion years ago.
The farthest galaxy identified in the image is 13.1 billion light-years away. It formed less than a million years after the universe began. NASA is confident that a systematic examination of the image will reveal older, more distant galaxies.
Some of SMACS 0723’s galaxies are egg-shaped elliptical galaxies. Those galaxies are older results of galactic collisions. Some of them are spirals, which suggests that they have not undergone collisions with other cluster galaxies.
Now you can look for galaxies that seem to be merging or colliding. As they rip stars away from each other, they slingshot some of their stars into the space between and around the galaxies.
Look for the halo of white light within and around the galactic cluster. That halo represents stars ejected from the galaxies because of galactic interactions.
Some astronomers hypothesize that the halo of stars around a galactic cluster contains up to half of its stellar mass. In other words, there may be as many stars in the cluster’s halo as in the galaxies that make up the cluster. The image provides visual evidence for that hypothesis.
Now zoom into any image section and notice the many fuzzy, red dots. Virtually all of them are not stars, but galaxies of stars.
Astronomer Harald Ebeling summed it up this way: “All the super faint, dark-red tiny dots, as well as many of the brighter, strangely shaped objects in this astounding image, are extremely distant galaxies that no human eye has seen before.”
Most impressive is the sheer number of curved red streaks in the image. They are galaxies at a far greater distance than the galaxies of SMACS 0723.
The more distant galaxies are usually invisible. They sit behind a brick wall, the cluster’s galaxies and the gas, dust, and stars between the cluster’s galaxies.
Gravitational lensing, an odd quirk of nature first predicted over 100 years ago by Albert Einstein in his General Theory of Relativity, allows us to see behind the galactic wall.
As the light from distant galaxies approaches the galaxy cluster, some of the light is bent around the cluster, just as light is bent when it passes through a lens.
SMACS 0723 has enormous mass. Enormously massive objects create enormous gravitational fields. Their gravity acts like a lens, bending some of the light from more distant objects around the cluster.
In effect, the gravitational field around SMACS 0723 is an enormous telescope. When JWST images the galactic cluster, it adds itself to nature’s most powerful optical system.
Lenses of any sort tend to magnify an image. Consequently, the galaxies look bigger than they would if the gravitational lens wasn’t there.
Gravitational lensing also curves the red galaxies into stretched-out arcs. A lens, even the gravitational variety, produces those curves images at the edge of its field of view.
Photographers, especially those amateurs who image the sky using lens-based telescopes, will recognize that trait as “curvature of field.”
Carefully compare the reddened galaxies, and you’ll notice that some of them are mirror images of other galaxies in the field. The galactic cluster’s gravitational field has split the light from a single galaxy. As it passes through different areas of the field, mirror images of the same galaxy result.
As I examine the image, I realize that the image is illusory, an image processing sleight of hand. The telescope collected the data in infrared light, and humans cannot see in the infrared.
Image specialists massaged the data to produce a simulacrum of what we might see in visible light.
The result is a melding of science and art that produced an image beautiful at first sight.
However, the image is also like a painting by one of the old masters. I know my appreciation of it will deepen with time and meticulous examination.
And that’s just from the first published image, somewhat hastily thrown together. If JWST manages to hold together against the harsh conditions in space, you ain’t seen nothing yet.
