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ALMA (ESO/NAOJ/NRAO); Rizzo et al.

Astronomers spy a Milky Way–like galaxy in very early universe

Astronomers imagine the early universe as a wild and lawless place, with chaotic fledgling galaxies full of swirling gases and frantic star formation. So an image released today comes as a surprise: a young galaxy, spied when the universe was just 10% of its current age, that looks remarkably like our calm and well-ordered Milky Way.

It’s not easy to make out galactic features across 12 billion light-years of space. That’s even true for the supersensitive Atacama Large Millimeter/submillimeter Array (ALMA), 66 radio telescopes high in the Chilean Andes that work together as a single instrument. But a team of astronomers used archival data gathered by ALMA in 2017 to take a look at a distant galaxy called SPT–SJ041839–4751.9, or just SPT0418–47 to friends, at a young age, 1.4 billion years after the big bang.

SPT0418–47 happens to have another galaxy in direct line of sight between it and Earth. The mass of that closer galaxy acts as a gravitational lens, bending SPT0418–47’s rays toward Earth so that ALMA can get a better image. That lensed image appears at first sight as a ring of fire (pictured). But the astronomers used computer modeling to reconstruct what SPT0418–47 really looks like. Reporting today in Nature, they reveal it has a rotating disk and a bulge around its center just like the Milky Way. Such features were thought to form much later in galactic evolution.

This and similar discoveries are pushing astronomers to look again at how galaxies can have evolved to an apparently mature stage in such a short time.