For the first time, scientists have discovered an extremely rare type of galaxy whose elliptical-like core is surrounded by two circular rings.
The galaxy, called PGC 10000714, is an example of what’s called a ring galaxy, where an external circle of young stars surrounds an older galactic core.
Closer inspection of the galaxy reveals its core is actually in the middle of not just one but two of those star rings, and it’s the first time that astronomers have encountered the phenomenon.
Approximately, 359 million light years away from the Earth, the galaxy appears to belong to a class of rarely observed, Hoag-type galaxies, researchers said.
Hoag’s object was discovered by astronomer Arthur Hoag in 1950.
Lead author Burcin Mutlu-Pakdil from the University of Minnesota at Duluth in the US said, “Less than 0.1 per cent of all observed galaxies are Hoag-type galaxies.”
Hoag-type galaxies are round cores surrounded by a circular ring, with nothing visibly connecting them.
The most common types of galaxies that we know about are broadly disc-shaped, with stars spread out either in a spiral formation like the Milky Way, or in an elliptical shape.
Galaxies with unusual appappearances give astronomers unique insights into how galaxies are formed and change.
“It was like spotting a snow leopard or some other rare and elusive animal,” astrophysicist Patrick Treuthardt from the North Carolina Museum of Natural Sciences said.
“A Hoag-type galaxy, one with a single circular ring surrounding a round core, is already very rare, but finding one with potentially two very regular rings is quite unique.”
Unlike disc-shaped galaxies in which stars are generally spread and scattered out, the stars in ring galaxies are divided into two distinct camps: a ring of young blue stars that shine very brightly on the outside, surrounding a well-defined core of older, less luminous stars in the centre.
The researchers collected multi-waveband images of the galaxy, which is easily observable only in the Southern Hemisphere, using a large diameter telescope in the Chilean mountains.
Analysis found that the outer ring of blue star is only about 0.13 billion years old, whereas the inner red is much more ancient, at approximately 5.5 billion years old.
To document this second ring, researchers took their images and subtracted out a model of the core. This allowed them to observe and measure the obscured, second inner ring structure, according to a study published in the Monthly Notices of the Royal Astronomical Society.
Galaxy rings are regions where stars have formed from colliding gas.
“The different colours of the inner and outer ring suggest that this galaxy has experienced two different formation periods,” one of the team, Burcin Mutlu-Pakdil, from the University of Minnesota Duluth explained in a statement.