A deep dive into Webb’s First Deep Field, the most detailed image ever of the early universe


posted Wednesday, July 13, 2022 at 10:59 AM EDT


After more than 20 years of effort from thousands of people, the public finally saw the first images from the James Webb Space Telescope yesterday. The first five images, including one spectrum graph, are stunning new looks at familiar celestial bodies, including galaxy clusters, nebulae, and even an exoplanet.

When NASA and its partners, including the European Space Agency (ESA), Canadian Space Agency (CSA), and the Space Telescope Science Institute (STScI), unveiled the images, we quickly shared them with a bit of background information. Now we want to look closer at each image and discuss the importance of each image and how they compare to images captured by the venerable and still operational Hubble Space Telescope.

First up is the image of the galaxy cluster known as SMACS 0723. President Biden previewed this image on Monday in a special surprise media briefing and then researchers discussed it in greater detail yesterday during the primary unveiling event.

Webb's First Deep Field (NIRCam). "Thousands of galaxies flood this near-infrared image of galaxy cluster SMACS 0723. High-resolution imaging from NASA’s James Webb Space Telescope combined with a natural effect known as gravitational lensing made this finely detailed image possible."

Credit: NASA, ESA, CSA, and STScI. Click here to view the full-resolution image.

This image is the deepest and sharpest infrared image of the distant universe ever captured. That alone makes it incredible. Better still, the image includes thousands of galaxies, including some of the smallest and faintest objects humankind has observed. The image is approximately the size of a grain of sand held at arm's length from the Earth's surface. Imagine holding that grain of sand between your fingers and then there are thousands of galaxies within that grain of sand. Quite frankly, it boggles the mind.

The tweet below from Alyssa A. Goodman, an astronomy professor at Harvard, helps illustrate how Webb's incredible quality allows us a better view of such a tiny sliver of the universe.

It's quite the improvement. However, what if we compare Webb to Hubble? After all, Webb's first image is reminiscent of images we've seen from Hubble. The Hubble Space Telescope has imaged SMACS 0723 before. In the video below from NuclearCraft, we see an image of SMACS 0723 as captured by Hubble compared to the new image captured by Webb.

There's no doubt that JWST has incredible image quality. What has this quality afforded scientists? The new image of galaxy cluster SMACS 0723 shows us how the cluster appeared 4.6 billion years ago. That's shortly before Earth even existed. We see many galaxies in front of and behind the primary cluster. Webb's resolving power brings into clear detail numerous star clusters and diffuse features for the first time.

Let's take a moment to appreciate that the image is such a distant look back in time. It's not the furthest back we've seen, but nonetheless, the light from the galaxies in the image took billions of years to reach us. In the distant reaches of the image, behind the cluster, we're looking back to about a billion years after the big bang occurred.

If you look at the arced galaxies in the image, this is due to the gravitational field of a galaxy cluster. It's causing gravitational lensing, which is when the gravity of a massive object bends light from objects behind it, like how a magnifying glass bends and warps images.

The incredible image, known as "Webb's First Deep Field," was captured using Webb's Near-Infrared Camera (NIRCam). It's a composite of images captured at different wavelengths and took roughly 12.5 hours. That's a relatively short period of observation.

The JWST team also captured the scene using Webb's Mid-Infrared Instrument (MIRI), and it's a slightly different but still impressive view of SMACS 0723. In the mid-infrared spectrum, the colors look quite different. In the left image captured by MIRI, if an object is blue and lacks spikes, it's a galaxy. If it has tiny spikes, then it's a star. Stars can also appear yellow. Red objects in the image could be distant galaxies or stars, as more research is needed. In the MIRI image, the most interesting color could be green, as this indicates a galaxy whose dust includes a mix of hydrocarbons and other chemical compounds. The MIRI image generally better illustrates where dust is, which is important when considering star formation. Using Webb's mid-infrared data, researchers will soon be able to precisely calculate the amount of dust in stars and galaxies, helping create better models and further understanding of how galaxies form and change over time.

SMACS 0723 as captured by MIRI (left) and NIRCam (right).

Credit: NASA, ESA, CSA, and STScI. Click here for the full-resolution image.

The JWST team also captured spectra using a pair of Webb's instruments. The Near-Infrared Spectrograph (NIRSpec) captured data from 48 individual galaxies simultaneously. It's a new technology that's never before been used in space.

The spectral data shows that light from the farthest galaxy in the deep field image traveled 13.1 billion years before Webb observed it. The universe itself is estimated to be 13.8 billion years. The image may have even more distant galaxies, as this was only an initial observation.

While the deep field image itself is of the most interest to the general public, spectra emission graphs get astronomers and astrophysicists very excited. The emissions show the chemical composition of galaxies in the early universe for the first time and may unlock key information about how galaxies form. Perhaps more importantly, comparing data from ancient galaxies against newer galaxies may help us understand how galaxies change over time and the universe's origins. We will soon know a lot more about galaxies throughout the cosmic timeline.

This data shows emission spectra from NIRSpec's micro shutter array. The instrument includes more than 248,000 tiny doors that can be opened individually to simultaneously gather spectra (light) data from up to 150 individual objects. NIRSpec gathered data from 48 individual objects from the SMACS 0723 deep field.

Credit: NASA, ESA, CSA, and STCsI. Click here for the full-resolution image.

There's also data from Webb's First Deep Field as captured by Webb's Near-Infrared Imager and Slitless Spectrograph (NIRISS). The incredible data shows that two of the arcs in the deep field image are not two separate, similar-looking galaxies but mirror images of the same galaxy. The Webb team writes, "By quickly examining the image at left by eye, it becomes clearer that one arc may be made up of two similar-looking galaxies. Their bright central regions match, despite their stretched appearances. These may be lensed galaxies – one galaxy that is mirrored in a second location. Are they the same? Researchers can’t be sure from the image alone – more data are needed to confirm a match."

The required data comes from NIRISS. Looking at spectra, we can see that the two arced galaxies exhibit the same composition, indicating but not proving that the galaxies are the same. However, data also indicates that the light from both galaxies was emitted 9.3 billion years ago, delivering the requisite evidence. A group of massive galaxies mirrored a single galaxy so that it appeared in the NIRCam image as two separate galaxies. This is one of many examples showing how the JWST's different instruments work together.

Webb's First Deep Field (NIRISS Emission Spectra)

Credit: NASA, ESA, CSA, and STScI. Click here for the full-resolution image.

Tomorrow, we'll take a closer look at a dying star's last hurrah before turning our attention to galaxy evolution, black holes, and a stellar nursery.