Astronomers Discover Incredibly Rare Double-Ringed Galaxy

Hoag's object, the first ring galaxy ever discovered. PGC1000714 is similar but has two rings. NASA/The Hubble Heritage Team (STScI/AURA)/Ray A. Lucas

Most galaxies in the universe follow a regular pattern but there are some rebels that are confident about rocking a different look. Astronomers have just discovered something very interesting about one of them. PGC 1000714 is a rare galaxy that has an elliptical core and is surrounded by two rings.

This galaxy belongs to the extremely rare class known as Hoag-type galaxies and is located 359 million light-years from Earth. The red core of PGC 1000714 is 5.5 billion years old, made by older stars, while the outer ring is full of young stars and is only about 130 million years old. 

By establishing the age difference between the ring and the core, the researchers discovered something unexpected: a diffuse red second inner ring closely surrounding the center of the galaxy. A detailed investigation of the object has been published by the Monthly Notices of the Royal Astronomical Society.

content-1483530817-researchersg.jpgFalse color image of Burcin's Galaxy (left) and a color map (Blue & infrared) which shows the two rings (right). Ryan Beauchemin

"The different colors of the inner and outer ring suggest that this galaxy has experienced two different formation periods," lead author Burcin Mutlu-Pakdil, from the University of Minnesota Duluth, said in a statement. "From these initial single snapshots in time, it's impossible to know how the rings of this particular galaxy were formed." 

The researchers suspect the outer ring formed from the gas of a smaller nearby galaxy that was slowly shredded apart. The origin of the inner disk instead remains a bit more mysterious, and the astrophysicists have stated that higher resolution observations are necessary to understand what exactly they are seeing here.

"Whenever we find a unique or strange object to study, it challenges our current theories and assumptions about how the Universe works. It usually tells us that we still have a lot to learn," added co-author Patrick Treuthardt, from the North Carolina Museum of Natural Science.

Hoag-type galaxies are less than 0.1 percent of all the observed galaxies and the peculiarity of having a double ring makes this a truly rare discovery.

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