Astronomers have discovered thousands of other galaxies with stars surrounding their main disks
PHOENIX — Thousands of newly spotted galaxies are dressed for a Victorian ball: in hoop skirts. The cache of “polar-structured galaxies” – with large starry or dusty structures oriented perpendicular to their main body – could help astronomers study how galaxies form and evolve.
“[Polar structure galaxies] are relatively rare in the universe,” said astronomer Jacob Guerrette in a press conference on January 5 at a meeting of the American Astronomical Society. Most galaxies keep their stars and gas fairly aligned with their main disks. Although astronomers have observed polar-structured galaxies since the 1970s, only a few hundred were known by 2024.
Now, Guerrette and his colleagues have identified about 3,000 new potential polar-structured galaxies in data from the Dark Energy Spectroscopic Instrument, or DESI, at Kitt Peak National Observatory in Arizona, increasing the number of known polar-structured galaxies by an order of magnitude.
“Based on these results, we estimate that about 2 percent of all nearby massive galaxies contain polar structures,” said Guerrette, of Brigham Young University in Provo, Utah. The Milky Way itself could also have a polar structure, Guerrette says, although it may be too faint to confirm.
Light from the most distant polar-structured galaxies in the DESI survey took about 7.8 billion years to reach Earth. Additional data from the Euclid Space Telescope added to the DESI cohort and extended the sample further in timemore than 11 billion years ago, the team also reported. The researchers hope to use the combined data sets to study the evolution of these galaxies over cosmic time.
Galaxies come in many shapes and sizes, and not all their polar structures are hoops. Some are streams of stars or gas; some look more like halos or bulges. But all these galaxies must have suffered clashes with one or more other galaxies in the past to acquire their equipment, Guerrette says. Indeed, in the absence of an external force, conservation of momentum keeps all the stars and gas in a rotating galaxy on roughly the same plane. The material orbiting at an acute angle to this plane must have been injected by an intruder.
This collision history makes polar-structured galaxies useful for probing global galaxy evolution. “Not all galaxies will have a polar structure,” says Guerrette. “But many galaxies will have undergone accretion or merger, so we can better study them in general through this smaller subset of polar-structured galaxies.”
