Extremely rare, dual ringed galaxy discovered in deep space

4 Jan 2017

Abstract ring illustration. Image: Dmitriy Rybin/Shutterstock

Astronomers have captured the first glimpse of a ringed galaxy more than 359m light years away that is so rare, it is believed to exist in only 0.1pc of the known universe.

Hoag’s Object – named after its discoverer and astronomer Arthur Hoag – is unlike many of the galaxies observed on a daily basis by the world’s array of telescopes.

With a well-defined elliptic core surrounded by two circular rings (which at first glance, do not appear to be connected), these galaxies differ from other standard ones that are disc-shaped, like the Milky Way.

To witness such a phenomenon, the research team, led by Burcin Mutlu Pakdil from the Minnesota Institute for Astrophysics, collected multi-waveband images of the galaxy, which is only easily observable in the southern hemisphere.

What really piqued the interest of the team was the discovery that the two rings are vastly different in age, with the blue outer ring believed to be approximately 0.13bn years old, compared with the red central core that could be 5.5bn years old.

“The different colours of the inner and outer ring suggest that this galaxy has experienced two different formation periods,” said Mutlu Pakdil.

Hoag galaxy

The left panel shows a false-colour image of PGC 1000714. The right panel shows a B-I colour index map that reveals both the outer ring (blue) and diffuse inner ring (light green). Image: Ryan Beauchemin

“From these initial single snapshots in time, it’s impossible to know how the rings of this particular galaxy were formed.”

‘We still have a lot to learn’

To help determine how these galaxies evolve, Mutlu Pakdil believes more images and data will have to be collected on the rare cosmic objects.

Yet based on what information we know, it has been suggested that the outer ring may be the result of this galaxy incorporating portions of a once nearby gas-rich dwarf galaxy. Any guess for the inner ring requires the collection of higher-resolution infrared data.

Co-author of the study, Patrick Treuthardt, added: “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.”

The team’s research, including the discovery of the PGC 1000714 galaxy, has been published in the Monthly Notices of the Royal Astronomical Society.

Colm Gorey was a senior journalist with Silicon Republic