Introduction: Galaxies Over Time

Our cosmic perspective has transformed dramatically since the early 1900s, when the Milky Way was viewed as a single "island universe" of stars. The pivotal moment came in 1923 when Edwin Hubble observed a Cepheid variable star in Andromeda, proving it was a separate galaxy far beyond our own. This discovery unveiled a cosmic vastness that fundamentally changed our understanding of the universe and our place within it.

Today, the Webb continues this tradition of discovery, pushing the boundaries of observable space and time to study galaxies across the entire history of the universe. Webb's infrared capabilities allow astronomers to peer back over 13 billion years, observing some of the first galaxies that formed after the big bang.

The image below is an infrared deep field captured by Webb in and around the same area as Hubble’s Ultra Deep Field. More than 45,000 galaxies are visible here, including some that existed when the universe was less than 600 million years old. Called JADES (JWST Advanced Deep Extragalactic Survey), this program devoted about 32 days of telescope time during Webb’s first year of science, into uncovering and characterizing faint, distant galaxies. The sheer number of these galaxies in this field is far beyond predictions from observations made before Webb’s launch. 

Click on the 4k resolution image immediately below (or click here for the maximum ~12k resolution) and zoom and pan through it to examine the diversity of galaxies within. 

In Depth: What is Webb Studying?

Early Galaxies

The Ancient Universe: A Different Cosmic Landscape

When Webb looks at very distant galaxies, it reveals a dramatically different universe than what we see today. Many of these ancient galaxies tend to be small and clumpy, often dominated by massive knots of intense star formation. This chaotic structure bears little resemblance to the organized spiral and elliptical galaxies that populate the modern cosmos.

The light from these earliest galaxies was emitted over 13 billion years ago and has been stretched to longer infrared wavelengths by the universe's expansion—which is precisely why Webb's infrared instruments are essential for studying these primordial eras. Through Webb's observations, astronomers have identified galaxies that existed less than 300 million years after the Big Bang, pushing our observational frontier to unprecedented depths.

Galaxy Evolution

The Galaxy Zoo: Diversity Across Time and Space

Galaxies are concentrations of stars, gas, dust, and dark matter that come in many varieties. Spiral galaxies like our Milky Way and Andromeda feature distinctive spiral arms and represent the majority of known bright galaxies. Elliptical galaxies appear more spherical from our Earth-based perspective and are often the result of galaxy mergers. Irregular clumpy galaxies have less structured forms and are typically smaller than their spiral and elliptical counterparts.

Webb has captured stunning examples of each type such this series of spiral galaxies including the face-on spiral NGC 4254 with its densely populated arms of glowing gas and forming stars.

Recent observations have also included the iconic Sombrero galaxy at both mid-infrared and near-infrared wavelengths, revealing its huge bulge and intricate structure in unprecedented detail.

Astronomers have reviewed Webb data to analyze a sample of 111 edge-on galaxies to dig into the structural origins of disk galaxies.

One of Webb's science goals is to understand how galaxies in the early universe formed and evolved into much larger galaxies like our own Milky Way. This requires identifying samples of galaxies at various evolutionary stages.

Below are some examples of galaxy variations the slideshow below (hover cursor over image to stop auto-advancing):

From Chaos to Order

The grand spiral and elliptical galaxies we observe today formed over billions of years through complex evolutionary processes. About 10 billion years ago, the universe was far more chaotic, with galaxies experiencing 10 times more star formation, frequent supernovae, and numerous mergers. Astronomers estimate that nearly all massive galaxies have undergone at least one major merger since the universe was 6 billion years old.

Webb is helping astronomers understand how these small, clumpy early galaxies evolved into the organized structures we see today. The telescope's spectroscopic capabilities reveal how chemical elements heavier than hydrogen were formed and accumulated as galaxy formation proceeded through the ages, providing crucial insights into the processes that shaped cosmic evolution.

Ongoing Mergers and Assembly: Galaxy Formation Never Stops

One of the most fascinating aspects of Webb's galactic research is demonstrating that galaxy formation and evolution continue in the present day. The telescope observes numerous examples of galaxies colliding and merging to form new structures, proving that the assembly process that began in the early universe remains active. Even our own cosmic neighborhood provides evidence of this ongoing evolution—the Andromeda galaxy is headed toward the Milky Way for a likely collision billions of years from now.

Recent discoveries like the Firefly Sparkle galaxy are providing direct evidence of how galaxies like our own Milky Way assembled through the gradual merger of distinct star clusters, each maintaining unique properties before eventual mixing. Meanwhile, studies of protoclusters like the Spiderweb are revealing how the largest cosmic structures grow through the accumulation of smaller galaxies, often heavily obscured by dust and gas.

Supermassive Black Holes

Webb's research addresses critical questions about supermassive black holes, which are thought to exist at the heart of all massive galaxies. Did these cosmic giants originate from huge early stars that collapsed to form the first black holes, which then merged over time? Or did clouds of gas in the early universe directly collapse to form massive black holes? Which came first, the black hole or the galaxy? Understanding the relationship between these central black holes and their host galaxies is crucial for comprehending galaxy evolution.

Webb is already shifting traditional ideas around how black holes form and grow. Take the Infinity Galaxy, which Webb observed in 2025 This galaxy was formed by the collision of two disk galaxies, resulting in an infinity shape made up of ring structures of stars around each galaxy. The nucleus of each galaxy is still visible, each with its own supermassive black hole. But between them, in a cloud of gas, appears to be a third, very active, supermassive, million-solar-mass black hole. Data from the Chandra X-ray Observatory and the Very Large Array also provide evidence for this supermassive black hole. It is extremely unusual. How did it get there? Scientists think it likely formed there, and pretty recently - which would mean we could be seeing the birth of a supermassive black hole for the first time. The gas within these colliding galaxies could shock and compress, forming a dense knot of gas that then collapses into a supermassive black hole. Though there are other possible explanations for the Infinity Galaxy black hole, the new data from Webb is strengthening the case that this is a newborn black hole formed by direct collapse. This science is still in progress, so stay tuned.

In 2026, Webb looked at an object called QSO1 existing just 700 million years after the big bang. The black hole within this object  is immense, ~50 million times the mass of the Sun, and it makes up for two-thirds of the object’s total mass. In other nearby galaxies, the supermassive black hole is only a tiny fraction of the host galaxy’s total mass. An object already this massive in the early universe (and without a substantial galaxy surrounding it) wouldn’t have had the time to form its black hole gradually from smaller stellar-mass black holes merging and feeding on nearby material. Webb’s measurements also showed that the gas around QSO1’s black hole is almost entirely hydrogen and helium, with almost no heavier elements present. Heavier elements are the by-products of star formation, meaning this object isn’t a galaxy rich with stars. It’s possible this is evidence for the existence of types of supermassive black holes that have only been theorized: either primordial black holes that formed in the first second after the birth of the universe; or ones formed directly from the collapse of a large gas cloud. It’s not yet clear from which process QSO1’s black hole resulted, but it was almost certainly born big, and might also be in the early stages of building a galaxy around itself.

Dark Matter

Webb's spectroscopic instruments are essential for determining galaxy rotation rates and masses, which reveal the presence of dark matter. When astronomers measure a galaxy's total gravitational mass needed to prevent it from spinning apart, they often find it far exceeds the visible matter. This invisible component—dark matter—makes up roughly five times more mass than normal matter in the universe.

Dark matter likely plays a key role in determining galaxy shapes and structures, serving as the invisible scaffolding upon which visible matter collects to form stars and galaxies. Computer models suggest that galaxies form when dark matter merges and clumps together in a hierarchical process where smaller structures combine to form larger ones—a process that continues today.

What you are (not) seeing, highlighted in blue in this image, is dark matter. In 2025, Webb was used to precisely map out the dark matter that is part of the makeup of two colliding galaxy clusters, with help from the Chandra X-ray Observatory. Webb captured more extremely faint galaxies in the Bullet Cluster than ever seen before (as well as foreground stars), allowing scientists to accurately determine the mass of the cluster. Chandra data shows the hot, X-ray-emitting gas present between the two galaxy clusters (highlighted in pink). As these two galaxy clusters collided, this gas was dragged out and left behind. Webb observations show that the dark matter (in blue) still lines up with the galaxies and was not dragged away.

Normally galaxies consist of gas, dust, stars, and dark matter, all combined, even when the galaxies are part of a cluster. Observing this separation between the gas and dark matter is unusual.

While we cannot see dark matter because it does not emit light, it has mass and gravitational influence on light we can see. It can act like a lens, magnifying and warping objects behind it. Imagine dark matter as water so clear you can’t see it unless the wind ripples it. The ripples will distort the shapes of any pebbles below its surface. Likewise, dark matter distorts the shapes of distant background galaxies. We can’t see it, but we see its effects.

Latest Images: Galaxies Over Time Theme

The image below is a SLIDESHOW of all NASA published imagery in the Galaxies Over Time theme.
USAGE: Hover over the image to see the image title and controls. Click the arrows to move through the slide show, click the image to go to a detail page with more info and the ability to download the image at various resolutions.