Astronomers have discovered thousands of previously unknown galaxies exhibiting unusual “polar structures” – essentially, starry or dusty formations extending perpendicularly from the main galactic disk, resembling Victorian-era hoop skirts. This finding, based on data from the Dark Energy Spectroscopic Instrument (DESI) and the Euclid space telescope, dramatically increases the known population of these galaxies and provides new avenues for studying galactic formation and evolution.
Discovery and Scale of the Phenomenon
For decades, astronomers have observed these peculiar galaxies, but their rarity limited detailed research. As of 2024, only a few hundred polar structure galaxies were cataloged. However, the recent analysis of DESI data has identified roughly 3,000 potential new candidates, increasing the known number by an order of magnitude.
Researchers now estimate that approximately 2% of all massive galaxies in the nearby universe possess these structures. This means they are far more common than previously thought. The newly observed galaxies span vast cosmic distances, with light from the farthest reaching Earth after traveling for 7.8 billion years. Euclid telescope data further extends the sample to over 11 billion years ago, allowing scientists to study how these structures evolve over cosmic time.
What Causes These “Hoop Skirts”?
The existence of polar structures isn’t accidental. Galaxies without external interference naturally rotate in a single plane due to the conservation of angular momentum. Polar structures indicate a past collision or merger with another galaxy, where material was forced into an orbit perpendicular to the original disk.
These structures take various forms: some are streams of stars, others resemble halos or bulges. Regardless, they all point to a violent cosmic history. The structures are a consequence of another galaxy disrupting the original system, forcing stars and gas into non-standard orbits.
Why This Matters
Polar structure galaxies serve as a valuable laboratory for studying galaxy evolution. While not all galaxies display these formations, many undergo mergers or accretion events. By studying this subset of galaxies with clear structural evidence of collisions, astronomers can gain broader insights into how galaxies grow and change over billions of years.
“Not every galaxy will have a polar structure,” explains astronomer Jacob Guerrette, “But a lot of galaxies will have gone through accretion or mergers, so we can better study those in general through this smaller subset of polar structure galaxies.”
The Milky Way itself may also exhibit faint polar structures, though confirming this remains challenging. The abundance of these structures suggests that galactic collisions are a more frequent occurrence than previously assumed, reshaping the universe in ways we are only beginning to understand.
This discovery highlights the dynamic and often chaotic nature of galactic evolution, and provides astronomers with a new tool to unravel the mysteries of cosmic history.
