Astronomers using the James Webb Space Telescope have identified an unusual galaxy from the early universe that seems to lack something scientists previously took for granted: rotation. Researchers report that galaxies are generally thought to begin rotating from the moment of their formation due to gravity and the streams of gas flowing into them. However, this distant galaxy, known as XMM-VID1-2075, shows no signs of such movement, making the discovery unexpected. The findings are described in a study published on May 4 in Nature Astronomy. Lead author Ben Forrest, a researcher in the Department of Physics and Astronomy at the University of California, Davis, stated that galaxies without apparent rotation are usually observed only much later in cosmic history. "This one in particular showed no sign of rotation, which was surprising and very interesting," Forrest said.
Early universe galaxy challenges established theories
Current models of galaxy formation argue that young galaxies should naturally rotate as they accumulate matter. However, over billions of years, repeated mergers between galaxies can disrupt or partially cancel out this motion. This process is thought to require an extremely long time. That is why astronomers were surprised to find a galaxy with such characteristics at a time when the universe was less than 2 billion years old. Nearby massive galaxies sometimes exhibit little organized rotation and contain stars moving in many random directions. Scientists typically link this behavior to galaxies that have undergone a long history of collisions and mergers.
Ancient galaxy had already stopped forming stars
Before using James Webb, Forrest and his colleagues in the MAGAZ3NE (Massive Ancient Galaxies at z>3 Near-Infrared) program had already observed XMM-VID1-2075 via the W. M. Keck Observatory. Previous observations revealed that the galaxy was already massive for its era, containing a multiple of the number of stars compared to our own Milky Way. The data also showed that it had almost stopped producing new stars. "Previous MAGAZ3NE observations had confirmed that this was one of the most massive galaxies in the early universe, with several times more stars than our Milky Way already, and also confirmed that it was no longer forming new stars, making it an extremely interesting target for further observations," Forrest said.
James Webb measured the galaxy's motion
The research team subsequently used James Webb to study XMM-VID1-2075 and two other galaxies from roughly the same era in greater detail. Webb allowed astronomers to measure how matter moves within each galaxy. "These kinds of studies have been done many times in nearby galaxies because they are larger and closer to us, so they can be examined from Earth. But it is very difficult to do this with high-redshift galaxies because they appear very small in the sky," Forrest explained. "James Webb is truly pushing the boundaries for this kind of research!" Of the three galaxies examined, one showed clear rotation, the second appeared more irregular, while XMM-VID1-2075 displayed random motions without overall rotation. "This is consistent with some of the largest galaxies in the local universe, but it was quite unexpected to see it so early in the history of the universe," Forrest stated.
Potential ancient galactic collision
Astronomers are now trying to understand how this galaxy transformed so quickly into what scientists call a "slow rotator." One possible explanation is that the galaxy collided with another galaxy that was rotating in nearly the opposite direction. Such an event could disrupt or cancel out much of the system's rotation. Researchers believe that Webb's observations may support this theory. "For this specific galaxy, we see a large excess of light on the side. This suggests the existence of some other object that entered and is interacting with the system, potentially changing its dynamics," Forrest said.
The search for other non-rotating galaxies
The team plans to continue the search for other galaxies like XMM-VID1-2075 in the early universe. Scientists will then compare these findings with computer simulations to better understand how galaxies evolved shortly after the Big Bang. "There are certain simulations that predict there will be a very small number of such non-rotating galaxies very early in the universe, but they consider them to be extremely rare," Forrest said. "This is a way to test these simulations and understand how common they actually are, which can then give us information on whether our theories regarding this evolution are correct."
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