Collisional Ring Galaxies and the Bullseye
Credit: NASA, ESA, Imad Pasha (Yale), Pieter van Dokkum (Yale)
Astronomers continue to unravel the enigmatic workings of the universe, shedding light on captivating phenomena. Among these are Collisional Ring Galaxies (CRGs), a distinctive class of interacting galaxies notable enough to warrant their own classification.
While the dynamics of galaxy interactions might suggest chaotic, amorphous outcomes, ring galaxies demonstrate otherwise, revealing a surprising order amid the complexity.
Analyzing the Bullseye Galaxy
In a recent study by Imad Pasha and collaborators [1], the spotlight falls on the Bullseye galaxy (also known as LEDA 1313424), offering a fresh insights into its present structure and future evolution. Utilizing the Hubble Space Telescope, the team identified nine concentric ring structures within this galaxy. Several of these rings are densely clustered near the galaxy’s core, while others span tens of kiloparsecs. Notably, two of the outermost rings are actively forming stars, encircling inner rings characterized by a striking reddish hue.
Complementary ground-based observations with the Dragonfly Telephoto Array revealed faint patches at greater distances. These observations hint of what may be a tenth ring that has gradually faded from view.
How they get their shape?
CRGs, like the Bullseye galaxy, emerge from rare head-on collisions, where a smaller galaxy plunges through the center of a more massive disk galaxy. This violent encounter triggers a density wave, generating expanding rings that ripple outward from the impact site.
Other CRGs
The Hubble Space Telescope and other observatories have documented additional examples of CRGs, each with its own remarkable features. The Cartwheel galaxy, for instance, boasts a brilliant outer ring teeming with star formation, connected to a central ring by faint, spiral-like arms of lower surface brightness [2]. Similarly, the Hoag’s Object presents an almost perfect ring encircling a yellow nucleus of old stars, contrasted by an outer ring rich with clusters of young, massive stars [3].
Another striking case is AM 0644-741, a ring galaxy whose shell-like structure gleams with bright stellar clusters [4]. At its heart lies a nucleus reminiscent of a pearl, the remnant core of what was once a typical spiral galaxy.
Image Credit -NASAThe possible future of the Bullseye Galaxy
Make it stand out
Observations of these and other CRGs suggest that their rings will continue to expand and dissipate over time, potentially evolving into a different class of cosmic structures: Giant Low Surface Brightness galaxies (GLSBs). Notable examples of GLSBs include UGC 1382—sometimes dubbed the “Frankenstein galaxy”—as well as Malin 1 and Malin 2, each characterized by their vast, diffuse profiles[6][7].
Though CRGs and GLSBs remain rare, astronomers anticipate that upcoming surveys with advanced facilities like the Large Synoptic Survey Telescope (LSST) and the Subaru Telescope will uncover more of these elusive systems, further illuminating the dynamic processes shaping our universe.
References
[1] https://iopscience.iop.org/article/10.3847/2041-8213/ad9f5c
Citation Imad Pasha et al 2025 ApJL 980 L3
[2] https://www.nasa.gov/universe/webb-captures-stellar-gymnastics-in-the-cartwheel-galaxy/
[3] http://sprite.phys.ncku.edu.tw/astrolab/mirrors/apod_e/image/1911/Hoag_HubbleBlanco_3000.jpg
[4] https://hubblesite.org/contents/media/images/2004/15/1520-Image.html
[5] https://hubblesite.org/contents/media/images/2002/21/1241-Image
[6] https://www.nasa.gov/image-article/frankenstein-galaxy/
