Astronomers using the James Webb Space Telescope have uncovered an unexpected feature in a distant, early galaxy. Despite forming when the universe was still very young, this galaxy shows no signs of rotation.
That behavior is typically seen only in very large, mature galaxies much closer to Earth, explained Ben Forrest, a research scientist in the Department of Physics and Astronomy at the University of California, Davis, and lead author of a study published May 4 in Nature Astronomy.
“This one in particular did not show any evidence of rotation, which was surprising and very interesting,” Forrest said.
Why Galaxies Are Expected to Spin
Current models suggest that galaxies begin spinning as they form. Gas flowing inward and the pull of gravity create angular momentum, setting these systems in motion.
Over billions of years, galaxies can collide and merge, especially in dense clusters. These repeated interactions can either build up or cancel out rotation. As a result, some nearby galaxies show little overall spin and instead display stars moving in random directions.
Because this transformation is thought to take a very long time, it is surprising to see it in galaxy XMM-VID1-2075 when the universe was less than 2 billion years old.
A Massive Galaxy That Formed Early
Forrest and his colleagues, part of the MAGAZ3NE (Massive Ancient Galaxies at z>3 NEar-Infrared) survey, had already studied this galaxy using the W.M. Keck Observatory in Hawaiʻi.
“Previous MAGAZ3NE observations had confirmed this was one of the most massive galaxies in the early universe, with already several times as many stars as our Milky Way, and also confirmed that it was no longer forming new stars, making it a compelling target for follow-up observations,” Forrest said.
Webb Telescope Reveals Internal Motion
Using the James Webb Space Telescope, the team examined XMM-VID1-2075 alongside two other galaxies from the same era. This allowed them to track how material moves within each system.
“This type of work has been done a lot with nearby galaxies because they’re closer and larger and so you can do these kinds of studies from the ground, but it’s very difficult to do with high redshift galaxies because they appear a lot smaller in the sky,” Forrest said. “(James Webb Space Telescope) is really pushing the frontier for these kinds of studies.”
Among the three galaxies, one clearly rotates, another shows irregular structure, and the third shows no rotation but strong random motion of its stars.
“That’s consistent with some of the most massive galaxies in the local universe, but it was a bit surprising to find it so early on,” Forrest said.
What Could Stop a Galaxy From Spinning
Researchers are now trying to understand how this galaxy became what scientists call a “slow rotator” so quickly.
One possible explanation is not a long history of multiple mergers, but a single dramatic collision. If two galaxies spinning in nearly opposite directions collided, their motions could cancel out.
“For this particular galaxy, we see a large excess of light off to the side. And so that’s suggestive of some other object which has come in and is interacting with the system and potentially changing its dynamics,” Forrest said.
Searching for More Spinless Galaxies
The team is continuing to search for similar galaxies in the early universe. By comparing observations with computer simulations, scientists can test whether current theories of galaxy formation hold up.
“There are some simulations that predict that there will be a very small number of these non-rotating galaxies very early in the universe, but they expect them to be quite rare. And so this is one way in which we can test these simulations and really figure out how common they are, and that can then give us information about whether our theories of this evolution are correct,” Forrest said.
Additional coauthors on the paper are: Brian C. Lemaux, UC Davis and Gemini Observatory, Hawaiʻi; Adam Muzzin and Adit H. Edward, York University, Toronto; Danilo Marchesini, Richard Pan and Nehir Ozden, Tufts University; Jacqueline Antwi-Danso, University of Toronto; Wenjun Chang, UC Riverside; M. C. Cooper and Stephanie M. Urbano Stawinski, UC Irvine; Percy Gomez, W. M. Keck Observatory, Kamuela, Hawaiʻi; Lucas Kimmig and Rhea-Silvia Remus, Ludwig-Maximilians-Universität München, Germany; Ian McConachie, University of Wisconsin-Madison; Allison Noble, Arizona State University; and Gillian Wilson and M. E. Wisz, UC Merced.
The research was supported by grants from NASA, the Space Telescope Science Institute, and the National Science Foundation.