ALMA sees most distant Milky Way look-alike

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have revealed an extremely distant and therefore very young galaxy that looks surprisingly like our Milky Way. The galaxy is so far away its light has taken more than 12 billion years to reach us: we see it as it was when the Universe was just 1.4 billion years old. It is also surprisingly unchaotic, contradicting theories that all galaxies in the early Universe were turbulent and unstable. This unexpected discovery challenges our understanding of how galaxies form, giving new insights into the past of our Universe.

CREDITS: European Southern Observatory (ESO)

“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,” says Francesca Rizzo, PhD student from the Max Planck Institute for Astrophysics in Germany. While the galaxy the astronomers studied, called SPT0418-47, doesn’t appear to have spiral arms, it has at least two features typical of our Milky Way: a rotating disc and a bulge, the large group of stars packed tightly around the galactic centre. This is the first time a bulge has been seen this early in the history of the Universe, making SPT0418-47 the most distant Milky Way look-alike.

“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,” says co-author Filippo Fraternali, from the Kapteyn Astronomical Institute, University of Groningen in the Netherlands. In the early Universe, young galaxies were still in the process of forming, so researchers expected them to be chaotic and lacking the distinct structures typical of more mature galaxies like the Milky Way.

Studying distant galaxies like SPT0418-47 is fundamental to our understanding of how galaxies formed and evolved. This galaxy is so far away we see it when the Universe was just 10% of its current age because its light took 12 billion years to reach Earth. By studying it, we are going back to a time when these baby galaxies were just beginning to develop.

This unexpected discovery suggests the early Universe may not be as chaotic as once believed and raises many questions on how a well-ordered galaxy could have formed so soon after the Big Bang. This ALMA finding follows the earlier discovery announced in May of a massive rotating disc seen at a similar distance. SPT0418-47 is seen in finer detail, thanks to the lensing effect, and has a bulge in addition to a disc, making it even more similar to our present-day Milky Way than the one studied previously.

Source: “ALMA sees most distant Milky Way look-alike” European Southern Observatory, 12 August 2020

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