Giant Rings Around Galaxies Perplex Astronomers
Astronomers have found unexpected rings and arcs of ultraviolet light around a selection of galaxies, four of which are shown here as viewed by NASA's and the European Space Agency's Hubble Space Telescope.
Credit: NASA/ESA /JPL-Caltech/STScI/UCLA [Full Story]

Giant rings of ultraviolet light have been spotted around some ancient galaxies, sending some scientists reeling from the completely unexpected phenomenon.?

The odd ultraviolet formations were spotted around several aged galaxies that astronomers had presumed to be astronomically dead ? inactive, that is.

"We haven't seen anything quite like these rings before," said researcher Michael Rich at the University of California, Los Angeles, in a statement. "These beautiful and very unusual objects might be telling us something very important about the evolution of galaxies." [Photo of the UV rings around galaxies.]

Astronomers observed the ultraviolet rings using two orbiting space observatories: NASA's Galaxy Evolution Explorer and Hubble Space Telescope. They studied 30 elliptical and lens-shaped "early" galaxies with strong UV emissions to determine why they ? though ancient and having no visible signs of star formation ? were still emitting such energetic light.

NASA announced the discovery this month. Details of the research appeared in the April 21 issue of the Astrophysical Journal.

Mystery rings in deep space

While young and lively galaxies have bluish hues from their active stars, older galaxies emit reddish collective starlight, NASA officials said in a statement. This reddish trait of the stars in the ancient galaxies allowed scientists to peg the ages of most of the stars at around 10 billion years old.

When astronomers studied the same galaxies with the Hubble Space Telescope, scientists discovered the source of the energetic look.

?Three-quarters of the galaxies were surrounded by tremendous shining rings of ultraviolet light. A few halos were so large they could fit several galaxies the size of the Milky Way, and had ripples in their glow that stretched across 250,000 light-years. ?

How do they exist?

Researchers have yet to explain how some of these galaxies received the infusion of fresh, cold gas needed to produce this light. One explanation, though unlikely, suggests that collisions between the older galaxies and smaller ones lent the gas, new stars or ring-structure directly.

"To create a density shock wave that forms rings like those we've seen, a small galaxy has to hit a larger galaxy pretty much straight in the center," said the study's lead author, Samir Salim, an astronomer at Indiana University in Bloomington."You have to have a dead-on collision, and that?s very uncommon."

Another idea is that the intergalactic medium, the thin material between galaxies, contributed gas and generated the rings with the help of bar-like structures at the center of some galaxies.

Ultimately, the striking observation proves that the cycle of galaxy birth and death has more to it than previously thought.

"In a galaxy's lifetime, it must make the transition from an active, star-forming galaxy to a quiescent galaxy that does not form stars," Salim said. "But it is possible this process goes the other way, too, and that old galaxies can be rejuvenated."??

Like recurring seasons, it may be that barren galaxies can be awakened to breed stars again in another ultraviolet soaked "summer," NASA officials said.