Spiral arms and bars were already pumping cold gas into galaxy centers nine billion years ago, new NOEMA and JWST observations reveal.
How did young galaxies keep their star factories running at full throttle, year after year, for billions of years? Welcome back to FreeAstroScience.com, dear friends. Whether you have followed us for years or just arrived from a search, we wrote this one for you. Two new studies, built on hundreds of hours of telescope time in the French Alps and razor-sharp images from the James Webb Space Telescope, have caught ancient galaxies in the act of refueling themselves. Stay with us to the end, and you will look at the night sky with different eyes.
Spiral arms and bars, the elegant structures that decorate galaxies like our own Milky Way, turn out to be working machinery: the NOEMA3D survey has measured cold gas flowing inward along these features in galaxies observed near cosmic noon, at speeds ten times higher than anything seen in the local universe, and at rates high enough to feed all their star formation.
What Was Happening at Cosmic Noon?
Cosmic noon, roughly 10 to 11 billion years ago, was the busiest construction era the universe has ever known. Star formation across the cosmos peaked then, running about ten times faster per unit volume than it does today, and the supply chain behind that boom was cold molecular gas. Galaxies at that epoch carried gas fractions of 30 to 60 percent of their baryonic mass. Nearby galaxies today scrape by on less than 10 percent.
The ten galaxies in the new study sit at redshifts between 1.1 and 1.6, which means their light traveled between 8 and 9.7 billion years to reach us. We see them as they were when the universe was only 4 to 5.5 billion years old. And they were prolific: their average star formation rate is 88 solar masses per year, dozens of times what the Milky Way manages now.
For decades, the textbook picture said these young galaxies were clumpy, chaotic messes, stirred up by constant mergers. In our own past coverage we happily repeated that line. This study tells us to retire it, and we are doing so here, in public. Major mergers account for only about 2 to 10 percent of galaxies at cosmic noon; the rest look like turbulent but well-ordered rotating disks.
How Do Spiral Arms and Bars Move Gas Inward?
Spiral arms and bars act like slow-motion traffic jams that steal angular momentum from the gas passing through them. A gas cloud orbiting a galaxy would circle forever if nothing disturbed it. When it crosses the gravitational ridge of an arm or a bar, it gets compressed, shocked, and torqued. Losing angular momentum means losing altitude, so to speak: the cloud drifts toward the galactic center, where it can form stars in the bulge or feed the central black hole, the same kind of monster we described in our guide to the true size of Sagittarius A star.
Astronomers already knew this mechanism operates in nearby galaxies. A 2022 survey of local disks showed that arms and bars concentrate gas in galactic centers and raise central star formation. The open question was whether the same machinery was installed and running during the universe’s peak production years, when disks were far more turbulent and gas-rich. Answering it required two things at once: sharp images of the structures and precise velocities of the cold gas. JWST delivered the first. NOEMA delivered the second.
What Did the NOEMA3D Survey Actually Measure?
NOEMA3D pointed the NOrthern Extended Millimeter Array, twelve antennas high in the French Alps, at ten massive star-forming disk galaxies and integrated for 18 to 62 hours per target between 2019 and 2025. The survey mapped carbon monoxide emission, the standard tracer of cold molecular gas, at a typical resolution of about half an arcsecond, fine enough to resolve structures a few thousand light-years across at those distances.
The analysis then followed a clear recipe:
- Map the CO emission and build velocity maps showing how fast the gas moves toward or away from us at every point in each galaxy.
- Fit each galaxy with an axisymmetric rotating-disk model using the forward-modeling code DysmalPy, which accounts for beam smearing and projection effects.
- Subtract the model from the data. Whatever survives, the velocity residuals, is motion that pure rotation cannot explain.
- Lay the residual maps over JWST near-infrared images and check where the leftover motion lives.
All ten galaxies rotate in an orderly way, with a median turbulence of 32 kilometers per second and rotation speeds about 8.6 times larger than that turbulence. But in nine of the ten (the exception is a nearly edge-on system where the geometry hides such signals), the team found coherent patches of residual velocity. And those patches were not random. They traced the spiral arms and bars visible in the JWST images. In the best case, a giant spiral called G4_38065, the residuals on the western side follow the spiral pattern so cleanly that they appear tied to a bright, possibly infalling clump of gas.
The result, in the words of lead author Jean-Baptiste Jolly of the Max Planck Institute for Extraterrestrial Physics, provides compelling evidence that these structures were, in his words, “driving gas transport when the Universe was at the peak of its star-forming activity.”Jean-Baptiste Jolly, quoted by Universe Today, July 15, 2026
How Fast Is the Gas Flowing?
The in-plane radial flows reach 50 to 100 kilometers per second, and the net inflow rate averages about 50 solar masses per year, comparable to each galaxy’s star formation rate. Fifty solar masses. Every year. To put that in perspective, a flow like that would deliver the entire molecular gas reservoir of the present-day Milky Way, several billion solar masses, in under 200 million years, a blink on cosmic timescales.
| Property | NOEMA3D galaxies, 8–9.7 billion years ago | Typical nearby disk galaxies |
|---|---|---|
| Cold gas fraction | 20–48 percent of baryonic mass | Below 10 percent |
| Radial gas flow speed | 50–100 km/s | Below 5 km/s in simulations of local barred galaxies |
| Net gas inflow rate | Around 50 solar masses per year, of order the star formation rate | Far smaller, slow secular trickle |
| Gas turbulence | Median 32 km/s velocity dispersion | Much lower, dynamically colder disks |
We owe you the honest caveats too. Separating true radial inflow from gas streaming along elongated orbits is genuinely hard, especially near a bar, so part of the measured signal could be tangential motion in disguise, and the team says so plainly. The spatial resolution also cannot yet distinguish inflow along an arm from outflow in the gap between arms; if both coexist, the true speeds would be even higher, not lower. Science earns trust by stating what it does not know, and this paper does.
Were Spiral Galaxies Really That Common Back Then?
Yes, and far more common than anyone expected before JWST. A companion study led by Juan Manuel Espejo Salcedo visually classified 1,451 massive star-forming galaxies imaged with JWST’s NIRCam camera in two epochs, one around redshift 1 and one around redshift 2.25. The verdict: 82 percent are disks. Among those disks, about half show spiral arms and roughly one in ten hosts a bar, with both fractions climbing as the universe ages. The team even found a mild surplus of three-armed spirals, about 30 percent of spirals versus 20 percent in the local universe (a small clue that gas-rich young disks favor slightly different spiral modes than mature ones).
The kinematics back the pictures up. Disks with spiral arms show rotation speeds around seven times their turbulence, and barred disks around five, exactly the dynamically settled behavior these structures need to survive.
We think this revision of the old chaotic-universe picture will stick. Two independent lines of evidence, morphology from JWST and gas kinematics from NOEMA, now point the same way, and independent agreement is the strongest currency in science.
Why Does This Change How We Think Galaxies Grew?
It moves the engine of galaxy growth from rare, violent collisions to steady internal plumbing. If arms and bars routinely pump 50 solar masses of gas per year into galactic centers, they can build central bulges, sustain star formation for billions of years, as we explored in our tour inside the W51 stellar nursery, and keep supermassive black holes fed during their fastest growth phase. That last point connects directly to our recent look at why supermassive black holes are starving today: the fuel lines that once ran at full pressure have since slowed to a drip.
The gas that arms and bars deliver has to come from somewhere, and the leading answer is continuous accretion from the cosmic web, the filaments of matter that lace the universe. In this picture, spiral arms and bars form the last segment of a supply chain stretching from intergalactic space down to newborn stars and hungry black holes. The new observations are the first direct measurement of that final segment in action at cosmic noon.
Confirming that these fast flows are universal will demand more of the same patient work: tens of hours per galaxy, one galaxy at a time.
Where Does This Leave Us?
A generation ago we imagined young galaxies as wrecking yards. Today we can watch them run as factories, with spiral arms and bars serving as conveyor belts that move raw material from the loading dock to the assembly line. Ten galaxies, hundreds of hours of millimeter-wave data, and the sharpest infrared eyes ever launched all tell the same story: the beautiful structures we admire in galaxy photographs were doing heavy industrial work nine billion years ago.
Next time you see an image of a grand spiral, remember that every arm is also a river.
This article was written specifically for you by FreeAstroScience.com, where complex scientific principles are explained in simple terms. Come back and visit us soon, and never turn off your mind, since the sleep of reason breeds monsters. Keep your curiosity alive.
Gerd Dani, President of FreeAstroScience — Science and Cultural Group
Frequently Asked Questions
What is cosmic noon in astronomy?
Cosmic noon is the period roughly 10 to 11 billion years ago, about 2 to 3 billion years after the Big Bang, when the universe built stars at its fastest pace. The cosmic star formation rate density back then ran about ten times higher than it does today.
How do spiral arms and bars move gas inside galaxies?
Spiral arms and bars are gravitational structures that disturb the smooth rotation of a galaxy. They remove angular momentum from the cold gas they touch, which lets that gas drift inward toward the center. The new NOEMA3D observations show this process operating strongly around 9 billion years ago.
How fast does the gas flow in these distant galaxies?
The measured in-plane radial speeds reach 50 to 100 kilometers per second, with net inflow rates near 50 solar masses per year. Simulations of nearby barred galaxies predict averaged inflow speeds below 5 kilometers per second, so the cosmic noon flows run at least ten times faster.
Were spiral arms and bars common at cosmic noon?
Yes, far more common than astronomers expected. A JWST study of 1451 massive star-forming galaxies found that 82 percent are disks. Among those disks, about half show spiral arms and roughly one in ten hosts a bar, with both fractions rising as the universe grew older.
Why does gas inflow matter for supermassive black holes?
Gas that reaches a galaxy center does two things. It feeds new stars in the bulge, and it supplies the accretion disk of the central supermassive black hole. Inflow rates comparable to the star formation rate can explain how both bulges and black holes grew so quickly.
Sources
- Jolly, J.-B., Tacconi, L. J., Genzel, R., et al. (2026). NOEMA3D: Resolving radial gas flows in disk galaxies at z ∼ 1.1–1.6 with high-resolution CO observations. Submitted to Astronomy and Astrophysics. Preprint: arXiv:2604.18503
- Espejo Salcedo, J. M., Pastras, S., Vácha, J., et al. (2025). Galaxy morphologies at cosmic noon with JWST: A foundation for exploring gas transport with bars and spiral arms. Astronomy and Astrophysics, 700, A42. DOI: 10.1051/0004-6361/202554725
- Gough, E. (2026, July 15). Spiral Arms and Bars are Galactic Fuel Pumps for Star Formation. Universe Today.
