Researchers get first look at new, extremely rare galaxy

January 4, 2017
The left panel shows a false-color image of PGC 1000714. The right panel shows a B-I color index map that reveals both the outer ring (blue) and diffuse inner ring (light green). Credit: Ryan Beauchemin

Approximately 359 million light-years away from Earth, there is a galaxy with an innocuous name (PGC 1000714) that doesn't look quite like anything astronomers have observed before. New research provides a first description of a well-defined elliptical-like core surrounded by two circular rings—a galaxy that appears to belong to a class of rarely observed, Hoag-type galaxies. This work was done by scientists at the University of Minnesota Duluth and the North Carolina Museum of Natural Sciences.

"Less than 0.1% of all observed are Hoag-type galaxies," says Burcin Mutlu-Pakdil, lead author of a paper on this work and a graduate student at the Minnesota Institute for Astrophysics, University of Minnesota Twin Cities and University of Minnesota Duluth. 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 only easily observable in the Southern Hemisphere, using a large diameter telescope in the Chilean mountains. These images were used to determine the ages 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.

"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," says Patrick Treuthardt, co-author of the study and an astrophysicist at the North Carolina Museum of Natural Sciences.

Galaxy rings are regions where stars have formed from colliding gas. "The different colors of the inner and outer ring suggest that this galaxy has experienced two different formation periods," Mutlu-Pakdil says. "From these initial single snapshots in time, it's impossible to know how the rings of this particular galaxy were formed." The researchers say that by accumulating snapshot views of other galaxies like this one astronomers can begin to understand how unusual galaxies are formed and evolve.

While galaxy shapes can be the product of internal or external environmental interactions, the authors speculate that the outer ring may be the result of this galaxy incorporating portions of a once nearby gas-rich dwarf galaxy. They also say that inferring the history of the older inner ring would require the collection of higher-resolution infrared data.

"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," says Treuthardt.

An uncorrected proof of the peer-reviewed paper, "A photometric study of the peculiar and potentially double ringed, nonbarred galaxy: PGC 1000714," was published online in the Monthly Notices of the Royal Astronomical Society by Oxford University Press on Nov. 30, 2016.

Explore further: Image: Hubble's view of the polar ring of Arp 230

More information: Burcin Mutlu Pakdil et al, A photometric study of the peculiar and potentially double ringed, nonbarred galaxy: PGC 1000714, Monthly Notices of the Royal Astronomical Society (2016). DOI: 10.1093/mnras/stw3107

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wduckss
1 / 5 (3) Jan 04, 2017
The rings are nothing new. We should pay attention to the center of the galaxy which has color. The color points to temperature of the central body. This is a novelty. Now (always) should centers of galaxies viewed as classic body (star) with mass, radius, rotation speed, temperature, etc.
Tuxford
1 / 5 (2) Jan 04, 2017
"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," says Treuthardt.

Indeed you do have a lot to learn. Hoagg objects are often simply a result of cyclic cosmic ray superwaves ejected from the core, according to Laviolette's model.

Elegant and simple. His model explains how concentric rings seem to be formed. It is just that the passing superwave illuminates the gas in the region it is passing through, similar to how the Crab is being illuminated right now by the last major superwave corresponding to our recent ice age. Synchrotron radiation is what we see in the Crab, as the Crab lies roughly on the radial line between Sag A and us, but further from Sag A than Earth by roughly 10-12 KLyrs (as I recall).

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