NASA’s Hubble Space Telescope has discovered an extraordinary sight in space! The massive galaxy known as LEDA 1313424 features nine rings full of stars, created when a smaller blue dwarf galaxy, referred to as an “arrow,” passed right through its center. Using the Hubble, astronomers identified eight distinct rings and confirmed a ninth ring with data from the W. M. Keck Observatory in Hawaii. Previously, other galaxies observed had a maximum of only two or three rings.
“This discovery was completely unexpected,” shared lead researcher Imad Pasha, a PhD student at Yale University in New Haven, Connecticut. “While reviewing images from a ground-based survey, I noticed a galaxy with several clear rings and felt compelled to investigate further.” The research team subsequently gave the galaxy the nickname “Bullseye.”
Follow-up observations with Hubble and Keck helped to determine which galaxy traveled through the Bullseye’s core — a blue dwarf galaxy located to its center-left. This small invasion occurred approximately 50 million years ago, leaving observable rings similar to ripples produced by a stone tossed into water. Although they are now 130,000 light-years apart, a faint trail of gas connects the two galaxies.
“We’re observing the Bullseye at a remarkable moment,” stated Pieter G. van Dokkum, a co-author of the study and a Yale professor. “A galaxy like this would only exhibit such a multitude of rings right after the impact.”
While galaxy collisions or close encounters happen often on cosmic scales, it is exceedingly rare for a galaxy to pass directly through the center of another. The blue dwarf’s straight path through the Bullseye triggered movements of material in waves, leading to new star formation in various regions.
How does the size of the Bullseye compare to our own Milky Way? The Milky Way measures about 100,000 light-years across, while the Bullseye spans nearly 250,000 light-years, making it two-and-a-half times larger.
Researchers utilized Hubble’s sharp vision to map out most of the rings’ locations, especially since many are concentrated in the core. “Without Hubble, this would have been impossible,” noted Pasha.
They employed data from the Keck Observatory to confirm an additional ring. The team suspects a possible tenth ring existed previously but has since faded away, estimating it could lie three times farther out than the broadest ring visible in Hubble’s images.
A One-to-One Match with Predictions
Pasha also discovered a remarkable correlation between the Bullseye and a well-known theoretical model: the rings appear to have spread outward almost exactly as predicted.
“That theory was put forth in anticipation of someone discovering so many rings,” van Dokkum remarked. “It’s very rewarding to verify this long-held prediction with the observation of the Bullseye galaxy.”
If viewed from a top-down perspective, it would be clear that the galaxy’s rings are not evenly spaced as one would expect on a dartboard. Hubble’s image presents the galaxy from a slight angle. “If we were to observe the galaxy from directly above, the rings would appear circular, with the innermost rings clustered together and gradually spacing out farther away,” Pasha clarified.
To envision how these rings formed, imagine dropping a pebble into a pond. The initial ring spreads outward, becoming the widest over time, while subsequent rings develop around it.
The researchers believe that the first two rings of the Bullseye formed rapidly and dispersed into wider circles. The additional rings may have emerged at slightly staggered intervals due to the more significant impact of the blue dwarf’s passage on the initial rings.
Although the orbits of individual stars remained largely unaffected, groups of stars accumulated to form distinct rings over millions of years. The gas was propelled outward and mixed with dust to create new stars, which further brightened the rings of the Bullseye.
There is still much to explore regarding which stars existed before and after the blue dwarf’s transit. Astronomers will now have the opportunity to refine models predicting how the galaxy might evolve over billions of years, especially regarding the potential loss of additional rings.
Though this remarkable finding was serendipitous, astronomers are eager to uncover more galaxies like this in the near future. “Once NASA’s Nancy Grace Roman Space Telescope begins its scientific operations, unique objects will become much easier to identify,” explained van Dokkum. “We will gain insights into how rare these extraordinary events truly are.”
