Researchers spot rare elliptical galaxy with two rings

Researchers have spotted for the first time an extremely rare type of galaxy whose elliptical-like core is surrounded by two circular rings.

Approximately 359 million light years away from the Earth, the galaxy appears to belong to a class of rarely observed, Hoag-type galaxies, the researchers said.

"Less than 0.1 per cent of all observed galaxies are Hoag-type galaxies," said lead author Burcin Mutlu-Pakdil from the University of Minnesota at Duluth in the US.

Hoag-type galaxies are round cores surrounded by a circular ring, with nothing visibly connecting them.

The majority of observed galaxies are disc-shaped like our own Milky Way.

Galaxies with unusual appearances give astronomers unique insights into how galaxies are formed and change.

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.

These images were used to determine the age of the two main features of the galaxy, the outer ring and the central body.

While the researchers found a blue and young (0.13 billion years) outer ring, surrounding a red and older (5.5 billion years) central core, they were surprised to uncover evidence for second inner ring around the central body.

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.

"We've observed galaxies with a blue ring around a central red body before, the most well-known of these is Hoag's object. However, the unique feature of this galaxy is what appears to be an older diffuse red inner ring," said the co-author of the study, Patrick Treuthardt, an astrophysicist at the North Carolina Museum of Natural Sciences.

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," Mutlu-Pakdil said.