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Astronomers have found our Milky Way’s galactic twin

Astronomers have spotted an oddity from the ancient universe: An extremely distant young galaxy which looks unexpectedly similar to our Milky Way.

The galaxy, known by the not terribly pithy name of SPT0418-47, is located so far away that light from it takes more than 12 billion years to reach us. This means that observing it is like looking back in time to when the universe was very young, at just 1.4 billion years old. And surprisingly, the galaxy looks remarkably like our own, much older galaxy.

Scientists had previously believed that all galaxies which formed in the early universe were chaotic and unstable, unlike our relatively sedate galaxy. But this new finding challenges that belief.

“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,” lead researcher Francesca Rizzo, Ph.D. student from the Max Planck Institute for Astrophysics in Germany, said in a statement.

an extremely distant galaxy that looks surprisingly like our Milky Way
Astronomers using ALMA have revealed an extremely distant galaxy that looks surprisingly like our Milky Way. The galaxy, SPT0418-47, is gravitationally lensed by a nearby galaxy, appearing in the sky as a near-perfect ring of light. ALMA (ESO/NAOJ/NRAO), Rizzo et al.

The image of the galaxy shown above appears in a ring shape due to the way in which the data about it was collected. As the galaxy is so far away, it is impossible to see using typical methods. So the team collected data with the Atacama Large Millimeter/submillimeter Array (ALMA) by using a nearby galaxy as a magnifying glass, with a technique called gravitational lensing.

Then, to see the distant galaxy as it actually exists, they reconstructed a realistically shaped image from this ring using computer modeling.

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

Reconstructed view of SPT0418-47
The research team reconstructed the distant galaxy’s true shape, shown here, and the motion of its gas from the ALMA data using a new computer modeling technique. ALMA (ESO/NAOJ/NRAO), Rizzo et al.

When looking at this reconstructed image, the researchers could tell that the galaxy was orderly and showed features similar to much older galaxies. “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,” co-author Filippo Fraternali, from the Kapteyn Astronomical Institute, University of Groningen in the Netherlands said in the statement.

This raises questions as to how such an orderly galaxy was able to form in the chaos of the early universe, and indicates that our previous assumptions about galactic evolution may be incorrect.

“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,” explained co-author Simona Vegetti, also from the Max Planck Institute for Astrophysics. “This result is quite unexpected and has important implications for how we think galaxies evolve.”

The findings are published in the journal Nature.

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