Washington, July 12: Scientists have discovered an enormous, bizarre galaxy possibly formed from the parts of other galaxies about 718,000 light-years away in an otherwise quiet neighbourhood.
More than seven times wider than the Milky Way, UGC 1382 is a "Frankenstein" galaxy that had originally been thought to be old, small and typical.
"This rare, 'Frankenstein' galaxy formed and is able to survive because it lies in a quiet little suburban neighbourhood of the universe, where none of the hubbub of the more crowded parts can bother it," said study co-author Mark Seibert from Observatories of the Carnegie Institution for Science.
It is so delicate that a slight nudge from a neighbour would cause it to disintegrate.
Seibert and Lea Hagen, a graduate student at Pennsylvania State University, University Park, came upon this galaxy by accident.
While looking at images of galaxies in ultraviolet light through data from NASA's Galaxy Evolution Explorer (GALEX), a behemoth began to emerge from the darkness.
"We saw spiral arms extending far outside this galaxy, which no one had noticed before, and which elliptical galaxies should not have," said Hagen who led the study appeared in the Astrophysical Journal.
It is one of the three largest isolated disk galaxies ever discovered.
But the biggest surprise was how the relative ages of the galaxy's components appear backwards.
In most galaxies, the innermost portion forms first and contains the oldest stars.
As the galaxy grows, its outer, newer regions have the youngest stars. Not so with UGC 1382.
"The centre of UGC 1382 is actually younger than the spiral disk surrounding it," Seibert said. "It's old on the outside and young on the inside. This is like finding a tree whose inner growth rings are younger than the outer rings."
More galaxies like this may exist, but more research is needed to look for them.
"By understanding this galaxy, we can get clues to how galaxies form on a larger scale, and uncover more galactic neighborhood surprises," Hagen noted.