This "Frankenstein" Galaxy Is Made Up Of Bits Of Other Galaxies

The galaxy in visible data (left), ultraviolet and deep optical data (middle), and low-density hydrogen gas (in green at right). NASA/JPL/Caltech/SDSS/NRAO/L. Hagen and M. Seibert

Astronomy is constantly improving, and for this reason it is worth always having a new look at old and familiar objects. And UGC 1382 is one such object. A seemingly boring small elliptical galaxy discovered in the 1960s, it turns out it is neither small nor elliptical and definitely not boring.

Using a series of multiwavelength surveys, astronomers discovered that UGC 1382, which is 250 million light-years from us, is actually a spiral galaxy stretching over 718,000 light-years, more than seven times wider than the Milky Way.

"We saw spiral arms extending far outside this galaxy, which no one had noticed before, and which elliptical galaxies should not have," said Lea Hagen, who led the study, in a statement. "That put us on an expedition to find out what this galaxy is and how it formed."

This led the team to make an outstanding discovery: UGC 1382 has formed the wrong way round.

"The center of UGC 1382 is actually younger than the spiral disk surrounding it," said study co-author Mark Seibert. "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."

Galaxies usually form from the inside out, with the core being made first and the spiral arms forming afterwards. A galaxy merger is the most likely explanation for UGC 1382’s curious composition; the galaxy is actually made of distinct parts that just came together billion years ago.

"This rare, 'Frankenstein' galaxy formed and is able to survive because it lies in a quiet little suburban neighborhood of the universe, where none of the hubbub of the more crowded parts can bother it," Seibert said. "It is so delicate that a slight nudge from a neighbor would cause it to disintegrate."

The full discovery is going to be published in the Astrophysical journal, and a pre-print is available online. UGC 1382 is now part of a class of galaxies called low-surface brightness, and although our instruments are getting better at detecting them, many more might be hiding in plain sight.

"By understanding this galaxy, we can get clues to how galaxies form on a larger scale, and uncover more galactic neighborhood surprises," Hagen said.



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