Scientists uncover rare 'Frankenstein' galaxy that is younger on the inside

Scientists have uncovered a "Frankenstein" galaxy that was possibly formed from parts of other galaxies and, remarkably, is younger on the inside than the outside. Galaxies ordinarily grow outwards, with innermost regions older and outmost younger. But UGC 1382 appears to be the reverse. Scientists said it may have resulted from separate parts forming independently before merging . In most galaxies,

the innermost portion is formed first, containing the oldest stars, and it grows outward with newer younger regions. But a new study to be published in the Astrophysical Journal said UGC 1382, located about 250 million light-years away at a size of more than seven times wider than the Milky Way, almost looked as though it were built out of spare parts.

"The centre of UGC 1382 is actually younger than the spiral disk surrounding it," study co-author Mark Seibert, of the Observatories of the Carnegie Institution for Science, 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.

"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 … it is so delicate that a slight nudge from a neighbour would cause it to disintegrate."

Scientists said the rare galaxy may have resulted from separate parts — two parts forming independently before merging together.

Dr Seibert and graduate student Lea Hagen came across the discovery by accident, searching for ordinary elliptical galaxies — which astronomers had originally thought UGC 1382 was.

But the pair looked at images of the galaxy in ultraviolet light through data from NASA's Galaxy Evolution Explorer, and saw "spiral arms extending far outside this galaxy, which no-one had noticed before, and which elliptical galaxies should not have".

"That put us on an expedition to find out what this galaxy is and how it formed," Dr Seibert said.

More galaxies like UGC 1382 may exist, the scientists said, but more research was 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 neighbourhood surprises," Ms Hagen said.