ALMA Spots Einstein Ring in Ancient Galaxy

Thanks to the Atacama Large Millimeter/submillimeter Array (ALMA) telescope, astronomers were able to spot an "Einstein ring" in an ancient, far-away galaxy - and no, it's not the famed Ring of Sauron from The Lord of the Rings trilogy.

Actually, this rare ring-like structure - forged by the chance alignment of two distant galaxies - is a unique display of gravitational lensing as predicted by Albert Einstein in his theory of general relativity.

Gravitational lensing occurs when a massive galaxy or cluster of galaxies bends the light emitted from a more distant galaxy, forming a highly magnified, albeit distorted image. In this case, the galaxy known as SDP.81 and an intervening galaxy line up so perfectly that the light from the more distant one forms a nearly complete circle as seen from Earth.

SDP.81 was first discovered by the Herschel Space Observatory, seen at a time when the Universe was only 15 percent of its current age. It is an active star-forming galaxy nearly 12 billion light-years away, while the closer galaxy it's being lensed by is comparatively only 4 billion light-years away.

"Gravitational lensing is used in astronomy to study the very distant, very early Universe because it gives even our best telescopes an impressive boost in power," ALMA Deputy Program Scientist Catherine Vlahakis said in a press release. "With the astounding level of detail in these new ALMA images, astronomers will now be able to reassemble the information contained in the distorted image we see as a ring and produce a reconstruction of the true image of the distant galaxy."

While other observatories have studied SDP.81 before, ALMA has provided the highest resolution images ever, capturing the remarkable details of the ring structure. Specifically, it achieved a maximum resolution of 23 milliarcseconds - that's the same as seeing the rim of a basketball hoop atop the Eiffel Tower from the observing deck of the Empire State Building.

"The exquisite amount of information contained in the ALMA images is incredibly important for our understanding of galaxies in the early Universe," added astronomer Jacqueline Hodge with the National Radio Astronomy Observatory in Charlottesville, Va.

The "Einstein ring" and these results will be described in further detail in an upcoming issue of the Astrophysical Journal, Letters.

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