Astronomers working with the James Webb Space Telescope report that a massive galaxy from the early universe shows no sign of spinning, a trait that theory says should not appear so soon after the Big Bang. In a study of the galaxy XMM-VID1-2075, a team led by the University of California, Davis found that the system, which formed when the universe was less than 2 billion years old, lacks the rotation that young galaxies are expected to carry from their formation. The finding was published May 4 in Nature Astronomy.
Why a still galaxy is a puzzle
Current models hold that galaxies begin turning as they take shape. Gas falling inward and the pull of gravity generate angular momentum, setting the whole system spinning. Over billions of years, galaxies collide and merge, and those repeated interactions can either reinforce or cancel out that rotation. Some nearby galaxies end up with little overall spin, their stars moving in random directions instead of along an orderly disk.
Because that transformation is thought to take a very long time, finding it already complete in the early universe is surprising. “This one in particular did not show any evidence of rotation, which was surprising and very interesting,” said Ben Forrest, a research scientist in the Department of Physics and Astronomy at UC Davis and lead author of the study. Astronomers call such systems “slow rotators,” and until now they were associated mainly with large, mature galaxies closer to Earth.
The galaxy itself was already an outlier. Earlier work had confirmed it as one of the most massive galaxies in the early universe, holding several times as many stars as the Milky Way, and had shown it was no longer forming new stars. That combination made it a compelling target for a closer look at how its internal material moves.
How the measurement was made
The observations came from the MAGAZ3NE survey, short for Massive Ancient Galaxies at z>3 NEar-Infrared, which had previously studied the galaxy using the W. M. Keck Observatory in Hawaii. For the new work, the team used Webb to examine XMM-VID1-2075 alongside two other galaxies from the same era, tracking how stars and gas move within each one.
That kind of measurement is routine for nearby galaxies, which are large and bright enough to study from the ground, but far harder for distant ones that appear tiny in the sky. Among the three galaxies the team examined, one clearly rotates, another shows irregular structure, and the third shows no rotation but strong random motion of its stars, a pattern Forrest described as consistent with some of the most massive galaxies in the local universe.
As for how a galaxy could stop spinning so quickly, the researchers point to one possibility that does not require a long history of mergers: a single dramatic collision. If two galaxies spinning in nearly opposite directions met, their motions could cancel. The team notes a large excess of light off to one side of XMM-VID1-2075, which Forrest said suggests another object has come in and may be altering the galaxy’s dynamics.
What it means and what remains open
The result matters because it offers a direct test of galaxy-formation models. Some simulations do predict a small number of non-rotating galaxies very early on, but expect them to be rare. Confirming how common they actually are would help show whether the current picture of galaxy evolution holds up. The team is continuing to search for similar systems and comparing what it finds against those simulations.
Several questions are still unresolved. The researchers have not established exactly what stripped the galaxy of its spin, and a single well-documented case cannot settle whether such galaxies are genuinely rare or simply hard to catch. The interpretation also rests on modeling the motion of stars in an object seen as it was more than 11 billion years ago, where measurements are difficult and uncertainties remain.
For readers following what Webb is revealing about the young cosmos, this is another example of the telescope finding mature-looking structures earlier than expected. The broader story to watch is whether more slow-rotating galaxies turn up at similar distances. If they do, theorists may need to revisit how quickly galaxies can settle into their final forms. The study was supported by NASA, the Space Telescope Science Institute, and the National Science Foundation.
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*This article was researched with the help of AI, with human editors creating the final content.
