Galaxy once thought to be tiny turns out to be gigantic

Astronomers observed spiral arms and low-density hydrogen gas surrounding the galaxy known as UGC 1382(Credit: NASA/JPL/Caltech/SDSS/NRAO/L. Hagen and M. Seibert)

Far away from our beloved Milky Way lies a galaxy called UGC 1382, a place that scientists and astronomers thought was just another tiny, elliptical galaxy. It turns out that not only is it bigger than they previously thought, but it's also much larger than the galaxy that Earth calls home.

Astronomers with the Carnegie Institution for Science ran a series of multi-wavelength surveys on the distant galaxy and discovered that it's actually a disk-shaped low surface brightness galaxy, the term for a galaxy that emits less light than normal galaxies. UGC 1382 is larger than Malin 1, the first and until now largest low surface brightness galaxy discovered back in 1986, with a diameter that is seven times bigger than the Milky Way.

Astronomers first cataloged UGC 1382 in the 1960s, but it wasn't until 2009 that anyone suspected that the galaxy might have some unique properties. Mark Seibert, an astronomer with the Carnegie Institution for Science, says the 2009 survey revealed that the galaxy might have had a rotating hydrogen disk, but the researchers who conducted the survey failed to follow up on their discovery.

"UGC 1382 came to our attention while we were looking at star formation in early-type galaxies using NASA's Galaxy Evolution Explorer," Seibert says. "We saw that in the ultraviolet part of the spectrum spiral arms were visible – something you do not expect to see around elliptical galaxies. Naturally, that finding sent us off on a very different path."

The new low surface brightness galaxy is not only larger than Malin 1 but it's also about 75 percent closer to Earth than Malin 1. Also, while UGC 1382 may be bigger than the Milky Way, both weigh roughly the same and contain the same amount of stars and gas.

Seibert says this discovery could helps astronomers and astrophysicists understand more about the evolution and formation of galaxies.

"We know that such objects need to have a low-density environment without other large galaxies nearby that would disturb it, but they also need a supply of small but gas-rich 'dwarf' galaxies to accrete and build the really large diffuse extended disk," Seibert says. "Unlike typical galaxy formation, however, the outer blue spiral disk appears to be older than the inner red disk. That is a big clue about how you get oddball giants like this."

A paper on the study will be published in the upcoming edition of the Astrophysical Journal.

Of course, astronomers are always finding new galaxies that have yet to be catalogued. Back in February, astronomers used an advanced multibeam receiver on the CSIRO Parkes radio telescope in Australia to identify 883 galaxies in a region 250 million light years away called the "Great Attractor," because it appears to be pulling the Milky Way and other galaxies towards it.

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