The Webb space telescope shows the galaxy GS18660 as it looked 2.1 billion years after the Big Bang, which makes it the most distant known ring galaxy.
The galaxy forms new stars equal to about 100 solar masses per year, mainly in the ring and in the core.
A small neighboring galaxy, which is moving away at 425 kilometers per second (about 264 miles per second) and is connected by a bridge of gas, is likely the one that created the ring.
The ring only showed up with Webb
The Webb space telescope has found the most distant known ring galaxy. It is called GS18660. The light that reaches us shows the galaxy as it looked 2.1 billion years after the Big Bang. The previous record holder, found in 2020, is closer to us.
Webb has already looked even further back in time. Among other things, the telescope has found two black holes that merged when the universe was 740 million years old.
The study is published in Astronomy & Astrophysics. The first author is Michele Perna, a researcher at the Centro de Astrobiología in Spain. The work is part of the Webb program GA-NIFS, which studies how galaxies grow.
The researchers were not looking for a ring. They chose the galaxy because it looked stretched out in older images from the Hubble space telescope. The ring was not clearly visible there. It only appeared when Webb's NIRSpec spectrograph was pointed at the galaxy. With the instrument, the researchers could study the galaxy's shape, how the hot gas moves, what the gas is made of and when the stars formed.
A ring full of young stars
The ring has a radius of about 3.5 kiloparsecs, roughly 11,000 light-years. Together, the stars in the galaxy weigh about 17 billion times as much as the sun.
GS18660 forms new stars equal to about 100 solar masses per year. Star formation takes place mainly along the ring and in the core. The ring alone forms several times more stars per year than the Cartwheel Galaxy, a well-known ring galaxy that lies much closer to us.
Between 10 and 20 percent of the stellar mass in the ring formed during the last few tens of millions of years. The gas in the ring is also moving outward at about 200 kilometers per second (about 124 miles per second). That fits with a wave spreading out from the center of the galaxy.
Traces of a collision
A ring of this kind usually forms when a small galaxy plunges straight through the center of a larger, disk-shaped galaxy. This sends a wave of dense gas outward, much like ripples in a pond. Where the gas is squeezed together, new stars form.
Near GS18660 there is a small neighboring galaxy. It is moving away from the large galaxy at about 425 kilometers per second (about 264 miles per second). A bridge of gas connects the two. The stars in GS18660 weigh about 100 times as much as the stars in the neighbor. The neighbor also sits roughly where an intruder would be expected after passing straight through the disk.
Based on the neighbor's speed and distance, the researchers estimate that the collision happened 17 to 42 million years earlier. That fits with the age of the youngest stars in the ring.
Michele Perna tells Live Science that a collision is the researchers' leading explanation. It is the combination of several clues that points that way: the neighbor, the gas bridge and the shape of the ring. The galaxy also has a structure that resembles a bar, and such bars can gather gas into rings. The researchers cannot yet fully rule out that explanation.
Rings are rare
In our part of the universe, only about one in 10,000 galaxies is a ring galaxy formed by a collision. Among distant galaxies, it has been hard to confirm the few candidates that have been found.
The find suggests that head-on collisions that create rings may have been more common in the early universe. If the collision is confirmed, estimates of how common such galaxies were back then will need to be revised, according to Perna.
Christopher Conselice is a professor of extragalactic astronomy at the University of Manchester and was not involved in the study. He describes the system as very unusual. He also finds it convincing that the galaxy has been through a collision or merger.
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