A massive galaxy formed less than two billion years after the Big Bang does not show an orderly rotation, contrary to expectations from models of galaxy formation. An ancient merger with another galaxy may have disrupted its motion.
Astronomers using the Webb Space Telescope have identified an unusual galaxy from the early universe that appears to be missing something scientists expect to find: rotation.
Researchers say the general consensus is that galaxies begin to rotate when they form, due to gravity and inflows of gas. But this distant galaxy, XMM-VID1-2075, shows no signs of this motion, making it an unexpected discovery.
Lead author Ben Forrest said that galaxies without significant rotation are typically seen much later in the history of the universe. "This one in particular shows no evidence of rotation, which is surprising and very interesting."
The galaxy from the early universe is surprising
According to current models of galaxy evolution, young galaxies should rotate naturally as they gather material. But after billions of years, repeated mergers between galaxies can disrupt or partially cancel this motion.
This process is thought to take a very long time. So astronomers were surprised to find a galaxy with these features when the universe was less than two billion years old.
Nearby massive galaxies sometimes show little organized rotation and instead contain stars moving in many random directions. Scientists usually attribute such behavior to galaxies that have had a long history of collisions and mergers.
A massive ancient galaxy that has already stopped forming stars
Before using Webb, Forrest and his colleagues in the MAGAZ3NE survey had already observed XMM-VID1-2075 using the Keck Observatory in Hawaii.
These early observations revealed that the galaxy was already huge for its time, with many times more stars than the Milky Way. The data showed that the galaxy had largely stopped forming new stars.
"Previous observations by MAGAZ3NE had already confirmed that this was one of the most massive galaxies in the early universe, already with several times more stars than the Milky Way, and also confirmed that it was no longer forming stars, making it a fascinating target for follow-up observations," said Forrest.
Webb measures the motion of galaxies
The researchers later used Webb to study XMM-VID1-2075 and two other galaxies from around the same time in more detail. Webb allowed them to measure how material moved within each galaxy.
"A lot of this kind of work has been done 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 look much smaller in the sky," Forrest said. "Webb is really pushing the boundaries of this kind of study."
Of the three galaxies examined, one showed a clear rotation, the other appeared less regular, and XMM-VID1-2075 exhibited random motion with no overall rotation.
"It's like some of the most massive galaxies in the local universe, but it's a bit surprising to find the phenomenon so early," Forrest said.
Astronomers are now trying to determine how this galaxy became what they call a "slow spinner" so quickly.
The researchers believe that Webb's observations could support this idea.
"In this particular galaxy, we see a lot of extra light on the side, which suggests that some other body has come along and is interacting with the system, perhaps changing its dynamics," Forrest said.
Short FAQ
What did the James Webb Space Telescope discover?
Webb identified that the galaxy XMM-VID1-2075, which formed less than two billion years after the Big Bang, shows no clear signs of orderly rotation.
Why is the discovery surprising?
According to accepted models, young galaxies should develop rotation as they gather material. Galaxies lacking orderly rotation are usually known from later stages in cosmic history.
What might explain the lack of rotation?
One possibility is that the galaxy underwent a collision or merger with another galaxy that was rotating in almost the opposite direction. Such an event could disrupt or cancel out a large part of the overall rotation.
What else is known about the galaxy?
Previous observations in the MAGAZ3NE survey and at the Keck Observatory showed that XMM-VID1-2075 was one of the most massive galaxies in the early universe, with several times more stars than the Milky Way, and that it had almost stopped forming new stars.
