'Ring of Fire' Galaxy From 11 Billion Years Ago Discovered

A "ring of fire" galaxy from the early universe has been discovered by astronomers. The galaxy, named R5519, is thought to have formed during a collision with another "victim" galaxy approximately 11 billion years ago—about three billion years after the Big Bang.

An image of R5519 shows the galaxy's unusual shape. It is a ring of stars with a hole at its center. Its mass is roughly the same as the Milky Way, but it is between 1.5 and two times larger. It is also forming stars at a rate about 50 times faster than our own galaxy. "Most of that activity is taking place on its ring—so it truly is a ring of fire," Tiantian Yuan, from the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions, Australia, said in a statement. "It is a very curious object that we've never seen before. It looks strange and familiar at the same time."

ring galaxy
Artist’s impression of the ring galaxy. The galaxy formed 11 billion years ago after a collision with another galaxy. James Josephides, Swinburne Astronomy Productions

According to NASA, about two-thirds of the galaxies we know about are spiral-shaped, such as the Milky Way. Some are elliptical-shaped, while the rest are unusual shapes, including rings. In the nearby Universe, collisional ring galaxies are roughly 10,000 times rarer than spiral galaxies.

Ring galaxies are thought to form through two different processes. Most are the result of internal processes. Rarer are those that form through collisions with other galaxies, with one galaxy smashing into the center of another galaxy composed of a thin disk.

In the early universe, however, galaxies were still forming. Spiral galaxies form over billions of years, with almost all massive galaxies having merged with at least one other since the universe was around six billion years old, NASA says. The first galaxies were small and "clumpy," the agency said, with "a lot of star formation occurring in the massive knots."

Yuan, who is lead author of a study about the discovery of R5519 published in Nature Astronomy, told Newsweek the ring galaxy was discovered "by accident." After wondering about its origin while working on other projects, she eventually started spending more and more time investigating until she "solved its puzzle." Data from the WM Keck Observatory in Hawaii, along with images from NASA's Hubble Space Telescope, led the team to conclude it was a type of "collisional ring galaxy"—the first to be discovered in the early universe.

"The universe creates collisional ring galaxies through cosmic shooting games," Yuan said. "You shoot a galaxy onto another galaxy, and those who can hit the bull's eye wins the title of collisional rings i.e. in order to create a 'ring of fire', we need a 'bullseye' collision first... In the nearby universe, they are rare because collisions are rare and you only have a few games going on to select such champions."

In the early universe, collisional ring galaxies were rare compared with the general galaxy population, she said. Some scientists believe there should be more collisional ring galaxies in the early universe because there would have been more chances of collisions than there are now. "We find that is not the case," Yuan said.

"The young universe might have more collisions and bullets, but it lacks thin stellar disks as the aiming board, and the cosmic environment is too chaotic to host such fine games. Imagine a shooting game with audiences running about and wind blowing... galaxies in the young universe are constantly being bombarded by moving satellites and swirling gas flows."

Yuan said the team now hopes to continue to study R5519 to find out more about its formation. "We don't know whether its ring is a first ring after collision or the second ring," she said. "Like throwing a pebble into a pond, the collision triggers consecutive rings, and the first ring is the brightest."