In November, astronomers Mutlu-Pakdil, Mangedarage, Seigar and Trueuthardt published a paper in the monthly notices of the Royal Astronomical Society where they stated that they had discovered an extremely rare galaxy. In the paper they presented a photometric study of PGC 1000714, a galaxy that resembles Hoag's Object because it has a complete detached outer ring, which has not yet been described in the literature.
This rare galaxy is located about 359 million light years from Earth. As the images show, it has a core of older stars that are then surrounded by a completely detached outer ring of newer stars. The older stars are differentiated from the newer stars by their color - they appear red whereas newer stars appear as blue. This unique structure suggests that this particular galaxy went through two different formation periods. At this time, it is not possible to know how this galaxy was formed exactly. The current theories about Hoag-type galaxies postulate that they form when two different galaxies collide. Because of the collision, a ring of gas, dust and stars forms and slowly begins to spread outward, like ripples in a pond.
This discovery is so exciting because, at this moment, only about 0.1% of galaxies that have been discovered thus far have this structure. As one of the authors of the study stated: "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."
Here's a video in which two of the main authors of the study discuss this new, exciting discovery:
Article by Rajmani Sinclair, January 12, 2017