Non-Rotating Galaxy found

 A giant galaxy that doesn’t spin is a surprise to astronomers     

Using instruments on the James Webb Space Telescope, astronomers can measure the movement of mass inside galaxies less than two billion years after the Big Bang. To their surprise, astronomers discovered a galaxy that is not rotating as would be expected at that age of the Universe. Astronomers using the James Webb Space Telescope have made a surprising discovery about a galaxy long, long ago and far, far away, It isn’t rotating. That’s something only seen in the most massive, mature galaxies that are closer to us in space and time, said Ben Forrest, a research scientist in the Department of Physics and Astronomy at the University of California, Davis, and first author of the paper.  Astronomers using the James Webb Space Telescope spotted something that shouldn’t exist, at least not so early in the universe. A massive galaxy, formed less than 2 billion years after the Big Bang, appears to have no rotation at all, a trait usually seen only in much older, evolved galaxies. This challenges current theories that young galaxies should still be spinning from their formation.

“This one in particular did not show any evidence of rotation, which was surprising and very interesting,” Forrest said. According to current theories, as the first galaxies formed, angular momentum from inflowing gas and the influence of gravity set them spinning. A giant ancient galaxy that mysteriously doesn’t spin is rewriting what we thought we knew about how galaxies form. Despite forming when the universe was still very young, this galaxy shows no signs of rotation. This behavior is typically seen only in very large, mature galaxies much closer to Earth, explained Ben Forrest. "This one in particular did not show any evidence of rotation, which was surprising and very interesting," Forrest said. The research was supported by grants from NASA, the Space Telescope Science Institute, and the National Science Foundation. Over many billions of years, some galaxies, especially those within galaxy clusters, merged with each other multiple times and their combined rotations added to or partly canceled each other. That’s why some galaxies which are closest to Earth (and therefore also relatively recent) can show little overall rotation but a lot of random movement of stars within them. This process should take an enormously long time, so it’s surprising that galaxy XMM-VID1-2075 had achieved this state when the universe was less than 2 billion years old. 

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.

Forrest and colleagues in the MAGAZ3NE (Massive Ancient Galaxies at z>3 NEar-Infrared) survey had previously observed this galaxy with 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. 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. 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.

The team were able to measure the relative movement of material inside them. 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. Of the three galaxies they sampled, one is clearly rotating, one is “kind of messy,” and one has no rotation but a lot of random motion, Forrest said. The XMM-VID1-2075 shows a lack of rotational movement compared to the other two galaxies. How did this galaxy become a “slow rotator” in less than 2 billion years? One possibility is that it is the result not of multiple mergers, but a single collision between two galaxies rotating pretty much in opposite directions. That idea is supported by the team’s observations. “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.

The astronomers are 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.