Webb telescope finds the most distant ring galaxy ever seen, likely shaped by a collision

Michele Perna, a postdoctoral researcher at the Spanish Astrobiology Center, led the team that turned the James Webb Space Telescope on GS18660 after older Hubble Space Telescope images showed a stretched-out shape. The telescope’s detailed observations uncovered a prominent ring that had been hidden from view.

The galaxy, seen as it appeared 2.1 billion years after the Big Bang, has a ring rich with newborn stars and is the most distant ring galaxy ever found. GS18660 also has a bar-like structure running north to south.

Scientists used JWST’s Near-Infrared Spectrograph to make the observations that revealed the ring. Their findings point to an encounter with a smaller companion galaxy, although the study describes the collision as a possible explanation for GS18660’s form.

The companion was moving away from GS18660 at about 264 miles per second (425 kilometers per second). Researchers also found a bridge of gas between the galaxies, with changing velocity along it.

Its position, roughly along GS18660’s minor axis, matches the location expected for an intruding galaxy after a head-on passage through the larger galaxy’s disk. The team estimated that the collision happened about 17 million to 42 million years earlier in the galaxy’s history.

Between 10% and 20% of the ring’s stellar mass formed in the past few tens of millions of years, the team estimated. That recent formation is consistent with the collision triggering star formation in a ring-like pattern.

Earlier estimates had suggested that collisional rings in the early universe were about as rare as they are today, around 1 in 10,000 galaxies. GS18660 therefore offers a view of a type of interaction that may have helped shape star formation in the young universe, and the observation hints that this period may have been more chaotic than once thought.

Perna is the study’s first author. Christopher Conselice is a professor of extragalactic astronomy at the University of Manchester in the U.K.

The study was published on 8 September in Astronomy & Astrophysics.