LOS ANGELES, Aug. 11 (Xinhua) -- Astronomers have found mysterious, giant loops of ultraviolet light in aged, massive galaxies, which seem to have a second lease on life, NASA's Jet Propulsion Laboratory (JPL) said on Wednesday.
Somehow these "over-the-hill galaxies" have been infused with fresh gas to form new stars that power these truly gargantuan rings, some of which could encircle several Milky Way galaxies, the JPL said in a news release.
The discovery of these rings implies that bloated galaxies presumed "dead" and devoid of star-making can be reignited with star birth, and that galaxy evolution does not proceed straight from the cradle to the grave.
"We haven't seen anything quite like these rings before," said Michael Rich, co-author of the paper and a research astronomer at University of California, Los Angeles. "These beautiful and very unusual objects might be telling us something very important about the evolution of galaxies."
The discovery was made through the combined power of two orbiting observatories, NASA's Galaxy Evolution Explorer and Hubble Space Telescope.
"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," the JPL news release quoted Samir Salim, a research scientist in the department of astronomy at Indiana University, Bloomington as saying.
"But it is possible this process goes the other way, too, and that old galaxies can be rejuvenated."
Astronomers can tell a galaxy's approximate age just by the color of its collective starlight. Lively, young galaxies look bluish to our eyes due to the energetic starlight of their new, massive stars. Elderly galaxies instead glow in the reddish hues of their ancient stars, appearing "old, red and dead," as astronomers bluntly say. Gauging by the redness of their constituent stars, the galaxies seen by the Galaxy Evolution Explorer and Hubble are geezers, with most stars around 10 billion years old.
Some ultraviolet starlight in a few of the observed galaxies might just be left over from an initial burst of star formation. But in most cases, new episodes of star birth must be behind the resplendent rings, meaning that fresh gas has somehow been introduced to these apparently ancient galaxies. Other telltale signs of ongoing star formation, such as blazing hydrogen gas clouds, might be on the scene as well, but have so far escaped detection.