Webb caught a galaxy several times the Milky Way’s mass — and it isn’t spinning

Webb has caught a galaxy with several times more stars than the Milky Way that is not spinning. Almost all the motion inside it is random, with stars moving every which way rather than streaming around a common axis. Slow rotators like this are familiar in today’s universe, where they appear as huge, evolved elliptical galaxies built up through long histories of merging. Finding one already in place when the cosmos was still in its toddlerhood breaks the assumption that this kind of galaxy needs many billions of years to form.

The team used the James Webb Space Telescope to map the internal motions of XMM-VID1-2075 and two other galaxies of comparable age. By tracking how material moves on opposite sides of each system, the astronomers compared organised spin against random stellar motion. XMM-VID1-2075 showed almost no measurable rotation, while the other two behaved like ordinary spinners.

For context, the Milky Way and most spirals are dominated by ordered rotation, with stars circling a flattened disc at hundreds of kilometres per second. Slow rotators look completely different. They are roughly spherical or football-shaped, with stars swarming chaotically. In the nearby universe, these are giant elliptical galaxies that took most of cosmic time to assemble through repeated mergers. Seeing one already finished when the universe was less than 2 billion years old means a galaxy can skip the slow ingredients.

The most likely shortcut, the team argues, is a single major merger. Two galaxies of comparable mass smashing into each other would scramble any pre-existing rotation and leave behind a system supported by random motion, essentially a fully formed elliptical built in cosmic minutes rather than over an eon. The case study suggests early-universe physics can compress galaxy assembly more aggressively than current models allow.

The result rests on three galaxies, only one of which is the headline case. Inferring the kinematics of whole galaxies at such distances involves model assumptions about dust, viewing angle, and how the Webb spectra translate to actual stellar motion. The astronomers are now searching for other early non-rotators to compare against. If XMM-VID1-2075 turns out to be an isolated outlier, single-merger formation stays a niche channel rather than a regular pathway.

The next phase, planned for upcoming Webb observing cycles, will widen the sample and let the team test the result against simulations of galaxy formation. The paper appeared in Nature Astronomy on 4 May 2026.