Do galaxies spin

On a clear night, under the sweep of the Milky Way, one might gaze at the faint blur of the Andromeda Galaxythrough a telescope. It appears as a misty spiral, majestic yet eerily still. This leads to a profound question: do galaxies truly spin and move, or are those swirling shapes merely static snapshots? Astronomers have long sought to determine whether these island universes are in motion, rotating like cosmic pinwheels or drifting serenely in space. The question isn’t trivial, it goes to the heart of how galaxies form, evolve, and even how the laws of physics play out on the grandest scales.

Pictured above: NASA Hubble Space Telescope image featuring the face-on spiral and Seyfert galaxy, ESO 420-G013

Credit: NASA/ESA/A. Evans (University of Virginia)/Processing: Gladys Kober (NASA/Catholic University of America)

To answer it, we must explore what constitutes “seeing” a galaxy spin. Unlike the hands of a clock, galaxies don’t complete a revolution in hours or days; their rotations take hundreds of millions of years. No human can watch a galaxy swirl in real time. Yet the universe leaves clues in light and matter that, when interpreted, reveal motion. Over the past century, scientists have gathered a wealth of observational evidence that galaxies are not static at all. They turn, wheel-like, around their centers, stars and gas arcing in orderly orbits. But how can we be so sure if we’ve never seen one make a full turn? The journey to that confidence is a story of ingenuity and wonder, one that bridges careful measurement and imaginative inference. It’s a story that includes bright-eyed astronomers like Edwin Hubble and Vera Rubin, mighty observatories from Mount Wilson’s classic telescopes to the modern James Webb Space Telescope (JWST), and even some deep cosmological puzzles that challenge our understanding.

Do galaxies spin? Exploring the cosmic dance of stars, gravity, and dark matter

As we unravel this story, we’ll also reflect on something more: what it means to “know” something in science. We’ll distinguish direct observation from extrapolation, examining how much of a galaxy’s spin is seen versus inferred. This scientific narrative will be interwoven with a sense of awe that transcends equations, a perspective influenced by voices as varied as the eloquent science communicator Carl Sagan, the visionary physicist Stephen Hawking, and the reflective Christian stargazer Trevor Jones. In their own ways, each found meaning in the cosmos, balancing scientific curiosity with spiritual wonder. So let’s embark on this exploration of spinning galaxies, a journey through history, technology, and philosophy, to understand how we know what we know, and to ponder what it ultimately means.

Early clues: From nebulous swirls to island universes

The idea that galaxies spin has its roots before we even knew what galaxies truly were. In the 18th century, philosophers like Immanuel Kant peered at faint “spiral nebulae” and speculated that these could be distant systems of stars, perhaps rotating slowly under gravity’s hand. At that time, they were just intriguing whirlpool shapes in primitive telescopes. By the late 19th and early 20th century, better telescopes revealed spiral patterns in objects such as the Whirlpool Galaxy (M51), suggestive of dynamic motion. Still, the nature of these spirals was hotly debated. Were they forming solar systems within our own galaxy, or were they “island universes”, separate galaxies far beyond the Milky Way?

A pivotal moment came in the 1910s. Astronomer Vesto Slipher at Lowell Observatory began measuring the Doppler shift of light from these spiral nebulae. The Doppler effect causes light from objects moving toward us to shift to bluer wavelengths and those moving away to redder wavelengths. Slipher observed that the great Andromeda Nebula (as it was then called) had a substantial blueshift, indicating it was moving toward us at about 300 kilometers per second, a staggering speed. Many other spiral nebulae showed redshifts, implying they were racing away. This was the first hint that these nebulae (soon to be recognized as galaxies) were not quietly sitting in space; they had significant motion. However, Slipher’s work mostly revealed galaxies’ line-of-sight motion (radial motion toward or away from us), not their rotation. It told astronomers that galaxies were indeed moving through space, and ultimately fed into Edwin Hubble’s 1920s discovery that the universe is expanding, with galaxies receding from one another. But whether individual galaxies were spinning was another question entirely.

In 1924, Edwin Hubble settled the debate on the nature of spiral nebulae by identifying Cepheid variable stars in Andromeda and calculating its distance, far beyond our Milky Way. Andromeda was a galaxy in its own right, a colossal system of stars. The universe suddenly became a lot bigger, populated with countless galaxies. With that understanding, astronomers started to think of galaxies as perhaps akin to the spinning disks of stars that Kant imagined. Yet actual evidence of rotation within a galaxy was still needed. One early clue came from the structure of spirals. Their pinwheel shape suggested a dynamic form, could it be that these arms were tracing a pattern caused by rotation? Astronomers theorized that spiral arms might be like cosmic traffic jams, dense waves moving through a spinning disk of stars and gas. If so, the galaxy had to be rotating to sustain such patterns.

The first tentative measurements of galactic rotation followed. In 1914, a young astronomer, Adriaan van Maanen, thought he observed the spiral nebula M101 rotate by comparing photographs taken years apart. He even estimated a rotation period of a few hundred thousand years, which was far too short. Unfortunately, this was an optical illusion of sorts, van Maanen’s claim was later refuted, and no actual rotation could be discerned in those images. The galaxy was simply too distant for any perceptible rotation over human timescales. It became clear that to “see” a galaxy’s spin, astronomers needed to rely on spectral measurements of velocity rather than direct images over time.

Hubble reveals Milky Way's dense nuclear star cluster

Credit: NASA, ESA, and Hubble Heritage Team (STScI/AURA, Acknowledgment: T. Do, A.Ghez (UCLA), V. Bajaj (STScI)

Our own galaxy’s spin: The Milky Way revelations

Before we look further out, consider the galaxy we know most intimately, the Milky Way. We reside inside it, which makes observing its overall rotation tricky, like trying to sense the spinning of a carousel while riding on it. In the early 20th century, astronomers were piecing together the Milky Way’s structure using star counts and distances. The realization that our Sun is not at the center of the Galaxy (thanks to Harlow Shapley’s work on globular clusters in 1918) set the stage for asking how the Galaxy moves.

The answer began to emerge in the 1920s. Jan Oort, a Dutch astronomer, used the motions of nearby stars to demonstrate that the Milky Way rotates. Building on theoretical work by his colleague Bertil Lindblad, Oort analyzed the Doppler shifts and proper motions of stars in different parts of the sky. In 1927, he published his analysis, which showed a clear signature of differential rotation, meaning the Galaxy is spinning but not like a solid wheel. Stars closer to the center orbit faster than those farther out, indicating a disk-like rotation. Oort derived constants (now known as Oort’s constants) that quantified the shear and rotation rate in the solar neighborhood. From this, astronomers could infer that the Sun takes about 225 million years to complete one orbit around the Galactic center. This period is sometimes called a “galactic year.” Indeed, the last time the Sun was at its current position in orbit, dinosaurs roamed the Earth, a humbling reminder of the immense timescales involved.

Observationally, Oort’s work was a triumph of inference. No one watched the Milky Way rotate, but by mapping stellar motions, Oort proved our Galaxy’s spin. In doing so, he overturned any lingering notion that the Milky Way was static. It rotates as a vast disk, our solar system hurtling along at roughly 220 km/s around the Galactic core. Later, the advent of radio astronomy in the 1950s provided an even more direct tool to map the Milky Way’s rotation. The discovery of the 21-cm emission line of neutral hydrogen allowed astronomers to trace gas clouds throughout the galactic disk, even on the far side obscured by dust. By measuring the Doppler shifts of this radio line at various longitudes, scientists constructed the rotation curve of the Milky Way, a plot of orbital speed vs. distance from the center. This revealed something intriguing: the orbital speeds did not drop off at the Galaxy’s outskirts as expected from visible matter alone. The Milky Way, like other spirals, has a “flat” rotation curve (more on that mystery soon). But the important point here is that by mid-20th century, there was no doubt anymore: our Galaxy spins, and we had measured its pattern of rotation, albeit indirectly.

Unveiling Andromeda’s secrets: First look at another galaxy’s spin

Armed with techniques honed on the Milky Way, astronomers turned to our nearest large galactic neighbor, Andromeda (M31), to see if it too rotates. Andromeda is a spiral galaxy very similar in shape to what we believe the Milky Way to be, just larger in diameter. If one galaxy spins, it made sense that others should as well. In the 1930s, an astronomer named Horace W. Babcock studied the Andromeda Galaxy and in 1939 published one of the first rotation curves for an external galaxy. Babcock measured the Doppler shifts of light from different parts of Andromeda’s disk, essentially peering at stars and gas on the approaching side (blue-shifted light) and the receding side (red-shifted light). He found that indeed one side of Andromeda is moving toward us, and the opposite side is moving away, consistent with a rotating disk. Babcock’s data hinted at rotation speeds of several hundred kilometers per second. However, he encountered a puzzle: the outer regions of Andromeda seemed to be moving faster than expected if the mass was concentrated in the galaxy’s visible stars. Babcock himself wondered if perhaps the luminosity underestimated the mass out in the fringes, or if new physics was needed. His work, ahead of its time, was a harbinger of the dark matter problem, though this wouldn’t be fully recognized until later.

Throughout the 1940s and 1950s, further evidence accumulated. Radio observations of Andromeda’s hydrogen gas confirmed the rotation and allowed measurements even beyond where stars are easily seen. By the 1960s, astronomers were gaining confidence that not only does Andromeda spin, but its rotation curve stays high even in the dim outskirts. Yet, the data were still sparse, and it took the meticulous efforts of Vera Rubin and her colleagues in the 1970s to truly cement our understanding of galaxy rotation on a larger scale.

Imagine peering at a galaxy through a spectrograph, which splits light into a rainbow of colors. Within that spectrum, certain dark lines appear, fingerprints of elements in stars and gas. If those lines are shifted towards blue or red, it signals motion. Vera Rubin, one of the few women in astronomy at the time, along with instrument maker Kent Ford, harnessed a new, sensitive spectrograph to measure these shifts in dozens of spiral galaxies. Rubin focused first on Andromeda, then on many other galaxies. What she found was revolutionary: the stars in Andromeda’s outer disk were moving just as fast as those much closer to the center. According to Newtonian gravity and the distribution of visible matter, one would expect orbital velocities to decrease with distance (much like planets in our solar system move slower the farther they are from the Sun). But the velocity profile of Andromeda remained nearly flat out to the furthest measured points. The galaxy was spinning in a way that defied expectations, unless there was a lot of unseen mass in its outskirts gravitationally boosting the speeds.

Rubin’s work, published in the late 1970s, provided the clearest evidence yet not only that galaxies do spin, but that they hold a mystery: dark matter. The inference was that Andromeda (and presumably other galaxies) is embedded in a vast halo of invisible matter, making up the majority of its mass, which keeps the rotation speeds high far from the center. It was a profound discovery. A simple question, “do galaxies spin?”, led to an unexpected answer: yes, they spin, and in doing so they reveal that most of their mass is unseen. In Rubin’s own humble way, she confirmed what earlier astronomers had hinted at. By extending rotation curves to the edges of galaxies, she showed definitively that galactic rotation is a real phenomenon, measurable and consistent, and that it points to new physics (or at least new ingredients of the universe).

One might wonder: did Rubin or anyone “see” the galaxy rotate? No, what she saw were spectra, graphs, and lines on a chart. Yet through those data, the motion of billions of stars was laid bare. In science, seeing is not always with eyes; sometimes it’s with careful reasoning and instruments that extend our senses. Rubin’s observations have since been repeated and expanded upon for thousands of galaxies. Today, a galaxy’s spin (quantified by its rotation speed) is a standard characteristic that astronomers measure, as routine as taking a person’s pulse. And just like a pulse can tell about a person’s health, a galaxy’s rotation curve tells astronomers about its mass distribution and vitality.

The Rubin revolution and the dark matter halo

The implications of Vera Rubin’s work were enormous. By confirming flat rotation curves in galaxy after galaxy, astronomers accepted that dark matter, whatever it was, must be present to explain the gravitational pull. To give context: in a typical spiral galaxy, stars orbit around the center under gravity’s pull. If most of the mass were in the visible stars and central bulge, the orbital speed of stars should decrease at large radii (just as planets far from the Sun move slower). Instead, Rubin’s data showed roughly constant speeds even far out, implying the mass enclosed keeps growing linearly with radius. The most straightforward interpretation is a massive halo of dark matter enveloping the galaxy, extending well beyond the visible disk.

It’s fascinating that by answering one question (“Do galaxies spin?”) we stumbled into another: “What comprises most of a galaxy’s mass?” Rubin’s results were met initially with some skepticism, could the instruments be misreading? But soon, other astronomers using radio telescopes to map hydrogen gas (which extends even further than the stars) saw the same effect. The rotation remained fast out to the furthest detectable gas. There was no denying it: galaxies are spinning much faster than their visible mass allows. This became one of the cornerstones of modern cosmology and led to the now widely accepted view that dark matter dominates galaxy dynamics.

From a direct observational standpoint, though, let’s highlight what Rubin did see: essentially, one side of a galaxy’s spectrum was consistently shifted towards blue, the other towards red. This is the telltale sign of rotation, the side spinning toward us is slightly bluer, the side spinning away is redder. We call this a Doppler shift signature of rotation. If galaxies were not spinning, or if their stars moved randomly without overall rotation, we wouldn’t see such a coherent pattern. Instead, we see it clearly. So in a sense, we have “seen” galaxies spin, not by watching their spiral arms turn, but by detecting the Doppler-imprinted rotation in their light.

The 1970s and 1980s cemented the idea that not only do galaxies spin, but spin is a fundamental property tied to how galaxies form. Theoretical work on galaxy formation suggests that as protogalaxies collapsed from the primordial gas of the early universe, they likely had slight net angular momentum (perhaps imparted by tidal forces from neighboring clumps). As a cloud collapses under gravity, it spins faster (like a figure skater pulling in their arms), a consequence of the conservation of angular momentum. Thus, galaxies were expected to rotate from birth. Rubin’s observations confirmed they indeed do, but also forced refinement of those models to include dark halos.

Importantly, not all galaxies are neat spirals with obvious disks. Elliptical galaxies, for example, are more spheroidal and often have stars on more random orbits. Do they spin? In general, ellipticals do have some rotation, but much less organized, they’re more like swarms of bees than a spinning frisbee. Some giant ellipticals rotate very slowly, and their support against gravity comes from the pressure of stellar motions rather than a coherent spin. Even so, careful studies have found that many ellipticals do have a slight net rotation or even embedded disks within them. Spirals, however, are the quintessential spinning galaxies, with a flat disk of stars and gas in rapid rotation around a central bulge.

How a spectroscope works

Credit: NASA Goddard/Shireen Dooling

Measuring the unseen spin: Techniques and triumphs

How do we measure the spin of a galaxy in practice? We’ve touched on the key method: spectroscopy. Let’s delve a bit more into that, because it’s one of the triumphs of human ingenuity that we can infer the motion of something millions of light-years away using just its light. When light from a galaxy is dispersed by a spectrograph, certain wavelengths appear either stretched (redshifted) or compressed (blueshifted) due to the Doppler effect if the source is moving relative to us. By aiming a spectrograph at different positions across a galaxy, say, the center, an edge along the disk, the opposite edge, astronomers can map out a velocity profile. Typically, one will see a gradient: perhaps at the galaxy’s center, things might be somewhat chaotic (lots of random motions in the bulge). Moving out into the disk along the plane, the velocity relative to us first rises, reaches a plateau, and then (as Rubin found) stays roughly constant or even sometimes rises slightly further out. This graph of velocity versus radius is the rotation curve. Each point on it was measured by looking at spectral lines (from stars or interstellar gas) at a given distance from the center and determining how shifted it was.

For nearby galaxies like Andromeda, we can target individual stars or stellar clusters. For more distant galaxies, we often rely on the glowing gas (for example, the bright emission line of hydrogen known as H-alpha can be used). In the radio band, the 21-cm line of hydrogen is superb because it’s abundant and can trace even the dim outskirts. Radio telescopes like those at NRAO or single-dish antennas in the mid-20th century scanned galaxies and produced rotation curves out to great extents.

Another method developed over time is integral field spectroscopy, where instead of measuring one slit across a galaxy, you obtain a spectrum at many points across the face of a galaxy simultaneously (using instruments with arrays of tiny lenses or fibers). This yields a detailed velocity field map of a galaxy, essentially, a picture where color coding shows the speed of rotation at each location. Such maps beautifully show one side of the galaxy in blues (approaching) and the other in reds (receding), vividly confirming rotation at a glance.

In the 1990s and 2000s, the Hubble Space Telescope also played a role in studying galaxy dynamics, albeit often in a different way. Hubble’s keen resolution allowed astronomers to measure the rapid rotation of gas very close to galactic centers, which led to the discovery of supermassive black holes. For instance, in the core of galaxy M87 and others, Hubble detected gas disks spinning so fast (hundreds of km/s within a few light-years) that only an enormous black hole’s gravity could explain it. These observations were essentially the same principle, Doppler shifts, but applied to the tiny inner region of galaxies. So Hubble confirmed spins on small scales (galactic nuclei), complementing ground-based and radio telescopes that charted rotation on galactic scales.

Meanwhile, surveys of galaxies expanded. The Tully-Fisher relation, discovered in 1977 by Brent Tully and Richard Fisher, provided a remarkable empirical link between a spiral galaxy’s rotation speed and its luminosity (hence its mass in stars). Essentially, the faster a galaxy spins, the brighter (and more massive) it tends to be. This relation became a tool to estimate distances (using rotation as a proxy for intrinsic brightness), but it’s also a kind of confirmation: spin is such a fundamental trait that it correlates with a galaxy’s very bulk properties. It’s akin to noticing that the faster a figure skater can spin, the larger and stronger they tend to be, not a perfect analogy, but illustrative that rotation is tied to a galaxy’s identity.

As technology advanced, we could measure rotation for galaxies farther and farther away (meaning earlier in time, since light takes time to travel to us). By the 21st century, spectrographs on large ground-based telescopes (like Keck, VLT, etc.) and space telescopes could probe galaxy rotation at significant redshifts, seeing if young galaxies in the early universe were rotating yet. These efforts found that even when the universe was only a few billion years old, disk galaxies existed and many showed signs of rotation. However, early disks were often more turbulent and clumpy, not as settled as today’s grand-design spirals. It suggested that galaxies gradually transformed into well-ordered rotating disks over cosmic time. That was the consensus view: small protogalaxies merge and spin up into larger disks over billions of years. Yet, as we’ll see, the James Webb Space Telescope has recently added some surprises to this story.

Before moving to those modern observations, it’s worth emphasizing: no one has yet directly visually witnessed a galaxy complete even a tiny fraction of a rotation. Our conclusions that galaxies spin rest on these ingenious measurements of velocity. It’s indirect, but extremely convincing, so much so that it’s considered established fact. This situation is not unusual in science. We often cannot observe processes on timescales of millions of years directly or phenomena beyond our immediate senses, but we gather evidence that builds a coherent picture. In the same way, we’ve never seen an electron with our eyes, yet we “know” electrons exist by their effects. We’ve never watched a mountain form in real-time, yet we know tectonic plates move by a few centimeters per year. With galaxies, we effectively catch them in the act of spinning by taking snapshots of their light and decoding those snapshots. It’s a bit like taking a long-exposure photograph of a starry sky, you don’t see the stars move moment to moment, but over hours they form trails. For galaxies, we can’t do a long exposure to see trails (they’re too slow), but spectroscopy gives us an instantaneous “trail” in wavelength space.

The limits of vision: Why we can’t watch a galaxy spin

It’s worth reflecting on why direct observation of galaxy spin is nearly impossible. The timescales are immense. A typical spiral galaxy might have a rotation period of, say, 200 million years at a radius like the Sun’s distance from the center. Even at the very edge, perhaps it takes half a billion years or more to go around once. In a human lifetime, the amount of rotation is minuscule. If you could live a hundred years and somehow see the whole galaxy at once, the stars would have moved only a fraction of a degree in their orbits, utterly imperceptible. The proper motion (actual angular movement on the sky) of galaxies’ internal parts is too tiny for current telescopes to detect over short times.

One exceptional case of “seeing” orbital motion is at the heart of our Milky Way. Over the past few decades, telescopes like the Keck Observatory have tracked individual stars near the Galaxy’s center (in the region of Sagittarius A*). These stars, called S2 and others, make very tight orbits around an unseen massive object, the black hole at the center. In a span of 16 years, star S2 was observed to go through a full elliptical orbit. So we have literally watched a star orbiting (and thereby proved the presence of a 4 million solar-mass black hole). But that’s a star around a black hole, not the whole galaxy’s rotation. It’s a dramatic example of orbital motion visible in a short time because the orbit is very small (a few light-days across) and the speeds are extremely high due to the black hole’s intense gravity. For a whole galaxy, scales are enormous and gravity is relatively weak at the outskirts, so everything moves leisurely.

We also can’t send out probes or mark a star’s position and come back millennia later to see movement. We’re inherently limited to the light arriving now. Therefore, our knowledge of galaxy spin comes from clever detective work, not direct cine-film of a galaxy spinning. Some might call it an assumption or extrapolation, and to an extent, it is an extrapolation of instantaneous measurements to infer a continuous motion. But it’s one supported by overwhelming evidence. Every spiral galaxy surveyed shows the same basic behavior: a systematic Doppler shift pattern indicating rotation. If galaxies didn’t actually spin, it would require an even more bizarre explanation for why their spectra are arranged just so (for instance, an elaborate pattern of random star motions conspiring to mimic rotation, which is wildly implausible).

In science, confidence grows from multiple lines of evidence. We have optical and radio rotation curves, we have correlations like Tully-Fisher, we have theoretical expectations from physics (angular momentum conservation) aligning with the data. So we say with confidence: galaxies do spin. Yet, it’s healthy to remember that it’s a conclusion drawn from inference. It’s similar to how we infer the Earth orbits the Sun, no one has watched an orbit from outside, but the seasonal shifts, parallax, and physics make it unquestionable. Likewise, we stand on our tiny cosmic timescale and pronounce that galaxies rotate, even though no person will ever personally witness one complete turn. It’s a testament to the power of scientific reasoning.

This distinction between direct seeing and inferred reality invites a philosophical musing. As humans, we often must trust evidence of things we cannot directly observe. In a way, it parallels aspects of faith: believing in the unseen because of the seen. One could draw an analogy that just as we infer an invisible mass (dark matter) sustaining the spinning galaxies, some infer an invisible hand behind the order of the cosmos. The two domains, science and faith, answer different questions, but they both grapple with evidence and belief in something beyond immediate perception. We will return to this reflection on the interplay of knowledge and wonder. For now, let’s advance to the cutting edge: how the newest telescopes have expanded our view of galactic spin and introduced new puzzles.

New eyes on the universe: Hubble and beyond

The launch of the Hubble Space Telescope in 1990 gave humanity a crystal-clear window to the universe. While Hubble’s primary triumphs were in imaging, think of the breathtaking Hubble Deep Field showing myriad distant galaxies, it also carried spectrographs that could be used to probe galaxy dynamics. Hubble’s observations confirmed rotation in many galaxies with high precision. For example, Hubble measured the rotation of disk galaxies in the Virgo Cluster to refine distance estimates and study their mass distributions. However, the real game-changer came in the 21st century with a suite of advanced telescopes and instruments. The Very Large Telescope (VLT) in Chile and the Keck telescopes in Hawaii, equipped with adaptive optics and powerful spectrographs, began to sample galaxy rotation in the distant universe (looking back 5 - 10 billion years in time). They found that many young galaxies were indeed rotating but often more chaotic, as mentioned. These observations supported the hierarchical formation model: small clumps form first, merge and spin up into larger, well-ordered disks later.

Enter the James Webb Space Telescope (JWST) in 2021, a new infrared observatory with unprecedented ability to see distant (high-redshift) galaxies. JWST was designed to peer deeper into the cosmic past than any telescope before. Early in its operations, JWST started picking up surprisingly mature galaxies at very high redshifts, meaning very far away, seen as they were only 300 - 500 million years after the Big Bang. These galaxies were not mere tiny blobs; some appeared massive and well-formed, perhaps even with disk-like structures. The astronomical community was astonished: how could such heavy and structured galaxies exist so early in the universe? According to the prevailing Lambda-CDM cosmology, the universe at that epoch (say redshift 10, roughly 500 million years old) should have had mainly small protogalactic fragments just starting to merge. Seeing objects with masses approaching that of today’s Milky Way so soon after the Big Bang was not expected.

One thing to clarify: JWST’s data on these earliest galaxies often come from their spectral energy distribution and photometry to estimate their stellar masses and ages. Direct rotation measurements of those very distant ones are extremely challenging (they’re just tiny red dots in JWST images). So, in those cases, we infer they likely have rotations because they might be disks, but we haven’t measured rotation curves for a galaxy at, say, redshift 10 yet. However, JWST has been able to measure rotation for some galaxies a bit less distant, for example, at redshifts around 3 to 6 (a few billion years post-Big Bang). JWST’s integral field unit on the NIRSpec instrument can take spectra of an entire galaxy at once. In a few cases, astronomers have reported JWST detecting velocity gradients in galaxies at redshift ~5 or 6, indicating rotation. There was even news of JWST identifying some spiral galaxies in the early universe and noting their rotation direction. A recent study intriguingly found an imbalance in the apparent spin directions of distant galaxies (more appeared to spin in one direction than the opposite in a certain survey). This was a puzzling observation, one that suggests either something fundamental (like a large-scale cosmic rotation or a complex bias in data). Researchers like Lior Shamir have suggested it could even hint at a large-scale anisotropy or simply be due to subtle observational biases as Earth moves. While this particular result is still debated, it underscores that we are now observing the spins of galaxies across a vast span of cosmic time, from near to far, and even looking for patterns in their orientations.

JWST has thus simultaneously affirmed and challenged our understanding. It affirmed that disk galaxies and rotation were already in place fairly early. For instance, one JWST finding was a massive disk galaxy at redshift 3.3 (about 2 billion years old universe) with a rotation speed and size comparable to today’s large spirals, essentially a fully formed, spinning giant when the universe was young. This was not a violation of physics, but it was at the surprising end of expectations, it implies in some regions, galaxy formation and rotation settling happened very rapidly.

On the challenging side, JWST’s discovery of many bright, apparently massive early galaxies led some to initially question if our cosmological timeline was off. Sensational headlines asked if the universe might be twice as old or if the Big Bang model was in jeopardy. These were likely overreactions; subsequent analyses provided more nuance. Some of those early galaxies might have their luminosity boosted by other factors like bursts of star formation or active black holes, meaning they weren’t as massive as they looked at first glance. Others might indeed be very massive, which suggests star formation and assembly can happen faster under the right conditions (for example, if dark matter halos and gas physics allowed quick collapse). None of this has yet overturned the basic idea that galaxies spin due to angular momentum. If anything, seeing disks so early confirms that as soon as galaxies exist, many take on a rotating disk configuration, exactly as theory would predict (just on a faster schedule than we assumed).

However, these JWST findings do stress-test our models of galaxy dynamics and formation. Perhaps the simulations need to allow for more efficient star formation at early times or initial conditions that yield higher angular momentum retention. It’s possible that the first generation of stars and gas settled into disks with surprising agility. Alternatively, some of those early “disks” might be something slightly different, like forming in high-density environments that streamline their spin-up.

Importantly, none of the JWST findings so far indicate that galaxies do not spin. Rather, they raise questions about how and when this spin was established. For instance, if a galaxy at 13 billion years ago is already a big rotating disk, maybe the conventional timeline of small mergers building up to big disks is not universal; maybe some big halos collapsed nearly monolithically into rotating structures. This might affect how we think about dark matter behavior or feedback from stars and black holes in the early universe.

CEERS Deep Field NIRCam: Webb Telescope unveils early galaxies bightened by black holes

Credits: NASA, ESA, CSA, S. Finkelstein (University of Texas)

Cosmological tensions: When observations challenge the models

The JWST early galaxies issue is part of a broader theme in cosmology: sometimes observations don’t neatly fit our standard model at first, causing what scientists call “tensions.” Another well-known tension is the Hubble constant discrepancy, different methods of measuring the universe’s expansion rate give slightly different answers, suggesting we might be missing a piece of physics. In the context of galaxy dynamics, the “unexpectedly mature early galaxies” found by JWST represent a tension with our expectations of structure formation timing. It’s as if the “galactic clock” in some parts of the universe was ticking faster than anticipated.

Does this undermine our confidence in our models of galaxy dynamics? It certainly challenges us to refine them. But it’s important to distinguish between surprise and revolution. Often in science, anomalies lead to deeper understanding without necessarily trashing the whole framework. For example, the flat rotation curves discovered by Rubin were a surprise that led to the dark matter paradigm. We didn’t throw out Newton’s laws; we posited a new component (dark matter) that preserves the laws. Similarly, with JWST’s findings, cosmologists aren’t abandoning the Big Bang or the idea that gravity drives galaxy formation. Instead, they are considering tweaks: maybe galaxies formed stars more efficiently early on, or maybe black holes in those early galaxies grew quickly and contributed mass or luminosity that we misinterpreted. Some studies have already shown that if you account for light from accreting black holes (active galactic nuclei) or dust-obscured star formation, the early galaxies might not be as monstrously massive as initial brightness suggested. In essence, the rulebook might not be broken, but we found a few new clauses we hadn’t considered.

From the perspective of galaxy dynamics specifically, the way galaxies rotate and evolve, these tensions make us ask: does dark matter behave as expected in the early universe? Cold dark matter theory suggests small halos merge into bigger ones gradually. If we see big halos early, could it be that dark matter clumped more quickly, or that there were variations in its distribution? Alternatively, could some modification of gravity (an idea some propose as an alternative to dark matter) better explain rapid disk formation? These are live debates in astrophysics. A few scientists have indeed taken JWST’s results as an opportunity to question the standard dark matter-driven model, suggesting perhaps more exotic scenarios. But so far, no alternative explanation has more evidence behind it; rather, the consensus is that our models need fine-tuning, not wholesale replacement.

There’s also the angle that we might be misinterpreting what JWST sees, those early galaxies might not be fully evolved systems; perhaps they are something like dense starbursting cores that will later become the centers of galaxies. In that case, we might be comparing apples and oranges with the local universe. Time and more data will tell. JWST is still relatively new, and with each month it gathers more data on distant galaxies, allowing statistical studies to see if early disks are truly common or just a few rare exceptions.

Another tension referenced by researchers analyzing spin direction (like the aforementioned study hinting most galaxies might spin one way) touches on the Cosmological Principle, the idea that on large scales, the universe is isotropic and no special directions. If a preferred spin direction were confirmed, it could imply a global rotation or anisotropy in the universe’s initial conditions. That would be a huge deal, potentially rewriting some fundamental assumptions. However, the majority of evidence from other observations (cosmic microwave background, large-scale galaxy surveys) still supports an isotropic universe. The spin-direction result is intriguing but needs independent confirmation. It might yet be due to subtle biases or a fluke of the sample. Still, it shows how measuring galaxy spins across the sky can potentially probe deep cosmological questions, far beyond the simple “does it spin” to “does the whole cosmos have a spin?”.

In summary, modern tensions have made astronomers appropriately cautious and curious. We’re confident galaxies spin, that’s firmly established. We’re less confident about whether our full storyline of how galaxies acquire their spin is correct in every detail. JWST has effectively asked, “Did some galaxies spin up faster than you thought? And if so, why?” These are exhilarating questions because they mean there is more to learn about the universe’s youth.

Knowing and wondering: Science, faith, and the spiral majesty

Step back for a moment from the technical details. Imagine yourself on a dark night, looking up at the hazy band of the Milky Way, or at an image of a distant spiral galaxy, its arms swirled like a divine fingerprint across the canvas of space. There is a moment of pure wonder in realizing that those graceful shapes are in fact colossal hurricanes of stars, spinning silently over eons. We have uncovered this truth with science, by patiently collecting photons and decoding their messages. Yet the emotional response, the sense of awe, goes beyond scientific data. It touches something primal in us: a mixture of curiosity and reverence.

Carl Sagan, gazing at billions of galaxies, often spoke about our place in the cosmos with poetic awe. He said, “Somewhere, something incredible is waiting to be known.” Discovering that galaxies spin was one such incredible thing. It transformed fuzzy patches in the sky into dynamic worlds. Sagan also famously reminded us that we are made of “star-stuff,” emphasizing an intimate connection with the cosmos. Think about it: the Sun orbits the center of the Milky Way, and in that grand rotation, it has completed maybe 20 or so circuits in its 4.5-billion-year life. Our planet and every atom on it have been carried on this galactic journey. In a sense, we are already riding a spinning galaxy, part of the cosmic dance without feeling it. That realization can evoke a deep sense of unity with the universe. As Sagan might encourage, we find that understanding the physics of a galaxy’s spin does not diminish its beauty, rather, it enhances our appreciation. The more we know, the more profound the mystery becomes.

Stephen Hawking, though a theoretical physicist, also contemplated what it means to comprehend the cosmos. In his quest for a unifying theory, he mused that achieving it would be a triumph of reason, “for then we would know the mind of God.” Hawking’s use of the word “God” was metaphorical, but it bridges to a spiritual sentiment: that understanding creation (in a scientific sense) is akin to touching something transcendent. When we consider galaxies spinning, governed by gravitation, one of the fundamental forces that Hawking studied, we are touching on those laws that have governed everything since the beginning of time. Hawking himself spent time considering the origin of the universe and the formation of galaxies in the context of cosmic inflation and quantum fluctuations. He understood the equations of rotation curves and dark matter halos, yet he also recognized that there’s a profound question of whythe universe is set up this way at all. His work and words exemplify that interplay of the explicable and the awe-inspiring inexplicable.

From a Christian faith-based perspective, the spectacle of a spinning galaxy can be deeply moving. The Bible speaks of the heavens declaring the glory of God (Psalm 19:1). For those who hold this belief, each galaxy, pinwheeling in space with its billions of stars, might be seen as part of that celestial declaration. The laws that cause a galaxy to spin could be viewed as ordained, a reflection of an orderly creation. Many devout scientists, including Vera Rubin, have expressed that studying the universe felt like an act of uncovering God’s handiwork. Rubin herself was known to be a person of faith; she once said, “In the absence of scientific data, I have faith.” She kept her religious views mostly private, but it’s known she was Jewish and found no conflict in embracing both science and spirituality. Similarly, an astrophotographer like Trevor Jones, spending nights capturing images of galaxies, often describes the experience in almost spiritual terms, patience, wonder, and the humbling realization of how vast creation is. Trevor Jones and others in his community might say that when you process an image of a spiral galaxy, knowing that each light dot is a star and that all those stars are circling a common center, you can’t help but feel a sense of worshipful awe, regardless of your specific creed. It’s the kind of awe that can lead one to quietly whisper a prayer of thanks or simply feel connected to something greater.

In weaving together these perspectives, we get a rich tapestry. On one thread, the scientific narrative: rigorous, technical, ever-questioning, it tells us how galaxies spin and with what evidence. On another thread, the philosophical and spiritual narrative: contemplative, meaning-seeking, it asks what it means that galaxies spin, and marvels at the existence of such order and grandeur. Blending them doesn’t diminish either. It’s like looking at the same masterpiece painting under two different lights: one reveals the fine brush strokes and technique (science), the other highlights the emotional hues and themes (faith and philosophy). Together, you see the full picture.

So, do galaxies spin? Yes, magnificently so. We’ve never watched a full rotation play out, but the symphony of evidence from a century of astronomy is unequivocal. From the subtle shifts in starlight measured by Vera Rubin, to the shimmering disks captured by the Hubble and Webb telescopes, all testify that galaxies are in motion. Each spiral galaxy is a colossal whirlwind of creation, moving according to physical laws that, as far as we can tell, hold universally. And in those very laws and motions, many find a source of inspiration that goes beyond mere facts, a hint of something poetic or divine.

We stand today both enlightened and humbled. Enlightened, because we’ve decoded one of nature’s grand secrets: the galaxies are engaged in an eons-long dance, spinning through the void. Humbled, because despite this knowledge, when we look up (or at an image on our screen of a distant galaxy) we can’t help but feel small and yet somehow significant, small in the face of cosmic immensity, but significant because we are participants and observers in this vast universe capable of understanding such things. As we continue to study galaxies, mapping their spins, probing their dark matter halos, and testing our cosmic models, we also continue an age-old human tradition: seeking our place in the cosmos.

In the cosmic ballet, galaxies spin and drift, cluster and collide. Stars are born and die within their spiral arms. New discoveries will surely come, perhaps solving today’s puzzles or uncovering new ones. Through it all, one can’t help but echo a bit of Sagan’s sentiment and a bit of the Psalmist’s: the more we uncover about spinning galaxies and the structure of the universe, the more we stand in wonder. Whether one’s mind turns to physics or to God, or, as for some, both, the spiral galaxies twirling in the darkness evoke a reverence for creation. The question “Do galaxies spin?” thus opens up not just a discussion of observational astronomy, but a meditation on knowledge itself. We infer the unseen from the seen, and we marvel at what those inferences reveal. Each galaxy, a swirling sermon in starlight, invites us to keep exploring with both our intellect and our soul, in a quest to comprehend this majestic universe we inhabit.

Pan video: Arp 184