Astronomers spot mysterious 'Frankenstein' galaxy

Scientists have uncovered a bizarre 'Frankenstein' galaxy possibly formed from the parts of other galaxies, located about 250 million light-years away.

A new study unveils the secret of UGC 1382, a galaxy that had originally been thought to be old, small and typical.

Instead, scientists using data from NASA telescopes and other observatories have discovered that the galaxy is 10 times bigger than previously thought and, unlike most galaxies, its insides are younger than its outsides, almost as if it had been built using spare parts.

"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 Mark Seibert from Carnegie Institution for Science in the US.

"It is so delicate that a slight nudge from a neighbour would cause it to disintegrate," Seibert said.

Seibert and Lea Hagen, a graduate student at Pennsylvania State University came upon this galaxy by accident.

They had been looking for stars forming in run-of-the-mill elliptical galaxies, which do not spin and are more 3D and football-shaped than flat disks. Astronomers originally thought that UGC 1382 was one of those.

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.

Researchers then looked at optical and infrared light observations from the other telescopes and build a new model of this mysterious galaxy.

UGC 1382, at about 718,000 light-years across, is more than seven times wider than the Milky Way, they found.

However, 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. It's old on the outside and young on the inside," Seibert said.

The unique galactic structure may have resulted from separate entities coming together, rather than a single entity that grew outward.

At first, there was likely a group of small galaxies dominated by gas and dark matter, which is an invisible substance that makes up about 27% of all matter and energy in the universe (our own matter is only 5%).

Later, a lenticular galaxy, a rotating disk without spiral arms, would have formed nearby.

At least 3 billion years ago, the smaller galaxies may have fallen into orbit around the lenticular galaxy, eventually settling into the wide disk seen today.

The study will be published in the Astrophysical Journal.