A very rare galaxy discovered 359 million light years away

A (very) rare galaxy has just been discovered by a team of physicists 359 million light-years from Earth. Of the Hoag type, it does not have one, but two circular rings surrounding the central bulb.

Do you know ring galaxies? The most emblematic is the Hoag object which gave its name to this type of galaxy of exceptional rarity since they represent only 0.1% of the galaxies known to date. Discovered by Arthur Hoag in 1950, this type of galaxy is distinguished by its very particular shape which was first taken for an Einstein ring by the discoverer. Then, by analyzing its redshift (Doppler effect), it was concluded that it was not a gravitational mirage, but a completely normal galaxy, although with a very atypical geometry. Physically, imagine a central bulge surrounded by a ring of stars with no connection between the two.

Scientists at the University of Minnesota, Duluth, and researchers at the Museum of Natural Science in North Carolina today announce the discovery of an even more unique Hoag-like galaxy. They indeed give a first description of this galaxy with an elliptical core in the center surrounded by not one, but two circular rings. PGC 1,000,714 (as it is called) is about 359 million light-years from Earth. Observations published today in the Monthly Notices of the Royal Astronomical Society report the presence of a blue outer ring of young stars (about 0.13 billion years old) surrounding a central core that turns red, about 5.5 billion years old. Researchers were surprised to find evidence of a second ring, an inner ring around the mid-colored central body. As Dr. Patrick Treuthardt, co-author of the study, suggests,  » the different colors of the inner and outer rings suggest that this galaxy had two different periods of formation « .

It is currently impossible to know how the two rings of this particular galaxy were formed. The authors speculate that the outer ring could be the remnants of a gas-rich dwarf galaxy that passed too close. Still, researchers hope to capture more snapshots of such galaxies to begin to understand how these unusual objects form and evolve. As Patrick Treuthardt says: “ Each time we discover a unique or strange object, it challenges our theories and assumptions about how the current universe works. We still have a lot to learn « .


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