Discovery of a Massive Ring Galaxy in the Early Universe
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Chapter 1: A Rare Find in Cosmic History
Astronomers have recently identified an extraordinary type of galaxy, referred to as a “cosmic ring of fire,” that dates back 11 billion years in the universe's history. This remarkable discovery challenges existing theories of galaxy evolution, as it indicates that massive ring galaxies could have formed much earlier than previously believed.
The gigantic cosmic doughnut, known as R5519, possesses a mass comparable to that of the Milky Way. However, it exhibits a star formation rate that is fifty times greater than our own galaxy, along with a stellar disc that is twice as expansive. This finding could provide valuable insights into when spiral galaxies, similar to the Milky Way, began to emerge in the cosmos. The details of this exciting discovery can be found in the latest issue of Nature Astronomy.
Lead researcher Dr. Tiantian Yuan from Australia’s ARC Centre of Excellence for All-Sky Astrophysics in 3 Dimensions (ASTRO 3D) describes R5519 as “a curious object” that has never been seen before, particularly in the context of the early universe. “Although it may not seem like a fitting analogy, R5519 resembles a corona galaxy, albeit it is distinct in nature,” she explains. “It appears both strange and familiar.”
One of the most striking features of this galaxy, located 11 billion light-years away from Earth, is the enormous void at its center. This gaping hole measures a staggering two billion times the distance between Earth and the Sun—three million times larger than the supermassive black hole photographed last year at the core of Messier 87 (M87).
“Our Milky Way lacks such a void; however, it does possess a significant Monoceros ring, likely the remnant of a dwarf satellite galaxy,” adds Yuan. “In contrast, R5519 contains a massive hole and a large ring that is radially moving.”
The implications of R5519 extend beyond its physical characteristics. Its existence during the early universe suggests that current models of galactic formation might require substantial reevaluation.
Section 1.1: Insights into Collisional Ring Galaxies
Observations indicate that R5519 is a 'collisional ring galaxy,' marking the first instance of such a galaxy being discovered in the early universe. This makes it not only rare but also significant, as existing models of galactic evolution suggest that massive galaxies should only have emerged around 6 billion years into the universe's 13.7 billion-year timeline.
“The occurrence of this galaxy type is rare under any circumstances, and even more so in the early universe,” remarks Professor Ivo Labbe, a co-author from Swinburne University.
“There are two primary categories of ring galaxies,” explains Yuan. “The first, commonly known as a ‘ringed’ galaxy, is the more typical type, with about 50% of spiral galaxies today exhibiting rings or partial rings. The second type, collisional ring galaxies, are exceedingly rare—only 1 in 10,000 galaxies evolves into this form.”
Yuan elaborates that most ringed galaxies form through internal processes, resulting from resonant motions within their galactic disks. “These ring structures typically emerge in areas where star orbits are densely packed due to orbital resonances related to spiral arms, bars, and ovals,” she notes.
In contrast, collisional rings are created via collisions, as their name implies. “When a galaxy strikes a target galaxy—a thin stellar disk—head-on, it creates a shockwave in the disk of the victim galaxy,” Yuan explains. “This pulse induces density waves that propagate radially through the target galaxy, forming a ring.”
These thin target disks are characteristic of spiral galaxies. Prior to their formation, these galaxies were chaotic, lacking the ordered spiral structure we observe today. Thus, this discovery suggests that disk assembly in spiral galaxies occurred earlier and over a more extended period than previously believed.
Section 1.2: The Rarity of Collisional Ring Galaxies
Yuan further explains that head-on collisions between galaxies are uncommon in the local universe, contributing to the rarity of collisional ring galaxies. However, such collisions were also thought to be infrequent in the early universe.
“Previously, scientists believed that we should find more collisional ring galaxies in the young universe due to a higher number of collisions,” Yuan states. “But our findings do not support this notion.”
Although the young universe may have seen more collisions, it lacked the thin stellar disks needed as targets, resulting in a chaotic environment that was unsuitable for such precise impacts. “Imagine a shooting game with players running amok and strong winds—conditions are far too chaotic,” Yuan compares. “This reflects how galaxies in the young universe were under constant bombardment from moving satellites and swirling gas flows.”
The discovery of R5519, a galaxy formed through these cosmic collisions, was a surprising revelation for the research team. “It was completely unexpected. This discovery suggests that thin stellar disks akin to our Milky Way’s existed for certain galaxies a quarter of the universe's age,” Yuan states. This finding opens new avenues in astronomy and cosmology, prompting questions about how various galactic structures first materialized. “Galaxies appear to evolve in stages; some components were assembled earlier than others,” she adds. “It is time for our models to advance to a higher level of precision and accuracy.”
Yuan concludes by noting that there are still many unanswered questions regarding R5519. “We still do not know whether this ring was the initial one formed after the collision or if it was a subsequent ring,” she shares. “I have obtained new data from the Keck telescope that will help us resolve these mysteries. That will be my next focus.”
This endeavor was fueled by her sheer curiosity: “I believe this discovery wouldn’t have been possible if I had simply followed the conventional path or succumbed to peer pressure. When I began working on this object, I had no idea where it would lead or what it might teach us.”
Yuan faced challenges in securing telescope time for her observations. “I had to ‘borrow’ time from my main project to pursue this object. I am very thankful for the support I received from my co-authors and colleagues,” she reflects. “Research driven by curiosity is crucial to me; it embodies the essence of why I pursue this field. Each observation reveals more pieces of the puzzle, making it increasingly challenging to align theoretical models with reality, and brings us closer to understanding the intricacies of nature.”
Special thanks to Dr. Tiantian Yuan
Original research: Yuan, T., Elagi, A., Labbe, I., Kacprzak, G. G., et al. ‘A giant galaxy in the young Universe with a massive ring,’ Nature Astronomy, [2020].
Chapter 2: Understanding R5519
The first video, "Huge Galaxy Ring Discovery Challenges Thinking On Universe," discusses how the discovery of R5519 is reshaping our understanding of galaxy formation and evolution.
The second video, "Ring Galaxies, Strangest and Rarest in the Universe, Explained...Except For One," further explores the characteristics and significance of ring galaxies, emphasizing their rarity and unique formation processes.