Milky Way Look-Alike Challenges Theories on Early Galaxy Formation

Astronomers have captured a ring of light from a distant galaxy that looks surprisingly like the Milky Way. (ALMA [ESO/NAOJ/NRAO], Rizzo et al.)

(CN) — A ring of light from a newly observed galaxy resembling the Milky Way, captured using the largest radio telescope system in the world, is making scientists rethink their theories on how galaxies are formed and evolve.

The galaxy is so far from Earth that its light has taken 12 billion years to reach the Atacama Large Millimeter/submillimeter Array’s star-gazing sensors in Chile, according to research published Wednesday in the journal Nature.

The portrait of the distant galaxy allows researchers to study its formation process when the universe was just 1.4 billion years old, or about 10% of its current age, according to a statement by study lead researcher Francesca Rizzo. 

The young galaxy — categorized as SPT0418-47 — doesn’t appear to have spiral arms like the Milky Way but it does share two notable characteristics with our galaxy: a rotating disk and a “bulge,” or cluster of stars grouped solidly around its galactic center.

The similarities surprised a team of researchers who captured images of the far-away galaxy using the ALMA.  

Rizzo said the discovery overturns scientists’ theories on galaxy formation because it demonstrates stable growth of a galaxy during a time in the early universe astronomers long believed was rife with turbulent development.

“This result represents a breakthrough in the field of galaxy formation, showing that the structures that we observe in nearby spiral galaxies and in our Milky Way were already in place 12 billion years ago,” said Rizzo, who is with the Max Planck Institute for Astrophysics in Germany.

Study co-author Filippo Fraternali said in the statement that because SPT0418-47 is so young, researchers expected it to be “chaotic,” or lacking the structures of more mature galaxies like the Milky Way.

“The big surprise was to find that this galaxy is actually quite similar to nearby galaxies, contrary to all expectations from the models and previous, less detailed, observations,” said Fraternali, from the University of Groningen’s Kapteyn Astronomical Institute in the Netherlands.

The image of SPT0418-47’s bulge is also the first time a galaxy’s central star-cluster has been imaged from this early in the history of the universe, according to the study, which is titled “A dynamically cold disk galaxy in the early Universe.” 

As young galaxies are too far away to observe closely with even the most powerful telescopes, researchers captured SPT0418-47’s portrait — which appears as a fiery ring of light around a dark center — using gravitational lensing. 

The effect is executed using a nearby galaxy’s gravitational pull as a powerful magnifying glass that bends distant light to ALMA’s sensors, causing it to look misshapen. 

In order to create a better portrait of the distant galaxy, researchers used computer modeling to reconstruct SPT0418-47’s true shape and the motion of its elements. 

“When I first saw the reconstructed image of SPT0418-47 I could not believe it: a treasure chest was opening,” Rizzo said.

The image is in clearer focus than the portrait by ALMA published in May of a massive rotating-disk galaxy formed more than 12 billion years ago.

Study co-author Simona Vegetti said researchers expect the galaxy to evolve differently from the Milky Way, evolving into a type of elliptical galaxy.

“What we found was quite puzzling; despite forming stars at a high rate, and therefore being the site of highly energetic processes, SPT0418-47 is the most well-ordered galaxy disc ever observed in the early Universe,” said Vegetti, also with the Max Planck Institute for Astrophysics. “This result is quite unexpected and has important implications for how we think galaxies evolve.” 

The European Southern Observatory, which is a partner in ALMA, will soon use its Extremely Large Telescope project to study whether young galaxies are as commonly less chaotic than predicted.

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