September 19, 2020

This ring of light is the most distant galaxy similar to our own ever observed.



An international group of astronomers has discovered an extremely distant and therefore very young galaxy, which is enormously similar to our own. It has been observed with the Atacama Large Millimeter / submillimeter Array (ALMA) that have the European Southern Observatory (ESO) and other institutions in the Chilean Atacama desert.

The galaxy is so far away that its light has been slow more than 12 billion years to reach us: we see it as it was when the universe was only 1.4 billion years old.

“This result represents an advance in the field of galaxy formation, showing that the structures we observe in nearby spiral galaxies and in the Milky Way were already in place 12 billion years ago,” says Francesca Rizzo, PhD student at the Max Planck Institute for Astrophysics in Germany, who led the research published today in Nature.

Although the galaxy studied, called SPT0418-47, does not appear to have spiral arms, it has at least two characteristics typical of ours: a rotating disk and a bulge, the large group of stars concentrated around the galactic center. It is the first time that a bulge has been seen at such an early stage in the history of the universe, thus making SPT0418-47 the most distant Milky Way-like galaxy observed to date.

“The big surprise was to discover that this galaxy is actually quite similar to nearby galaxies, contrary to what was expected from earlier, less detailed models and observations.”, co-author suggests Filippo Fraternali, from the Kapteyn Astronomical Institute of the University of Groningen, in the Netherlands. In the early universe, young galaxies were still in the process of formation, so the researchers expected them to be chaotic and lacking the typical structures of more mature galaxies like the Milky Way.

When the universe was 10% of its current age

Studying distant galaxies like SPT0418-47 is essential to understand how these types of systems formed and evolved. This galaxy is so far away that we see it when the universe was only 10% of its current age, as it took 12 billion years for its light to reach Earth. By studying it, we are returning to a time when these ‘baby’ galaxies were just beginning to develop.

Due to the great distance at which they are, it is almost impossible to observe these galaxies in detail, even with the most powerful telescopes, since the galaxies appear small and faint. The team overcame this hurdle by using a nearby galaxy as a powerful magnifying glass, an effect known as gravitational lens, allowing ALMA to see the distant past in unprecedented detail. In this effect, the gravitational pull of the nearby galaxy distorts and bends the light of the distant galaxy, causing us to see it warped and magnified.

Thanks to its almost exact alignment, the distant galaxy seen with gravitational lensing appears as a near perfect ring of light around the nearby galaxy. The research team reconstructed the true shape of the distant galaxy and the motion of its gas from the ALMA data using a new computer modeling technique. “When I first saw the reconstructed image of SPT0418-47, I couldn’t believe it: a treasure chest was being opened,” says Rizzo.

An unexpected order

“What we found was quite puzzling: despite forming stars at a high rate, and therefore being a place with highly energetic processes, SPT0418-47 is the best-ordered disk of galaxy that has ever been observed in the early universe.” stated the co-author Simona vegetti, also from the Max Planck Institute for Astrophysics. “This result is quite unexpected and has important implications for the way we think galaxies evolve.”

Astronomers note, however, that although SPT0418-47 has a disk and other features similar to those of the spiral galaxies we see today, they expect it to evolve into a galaxy very different from the Milky Way and join the class. elliptical galaxies, another type of galaxy that, together with spirals, inhabit the current universe.

This unexpected discovery suggests that the early universe may not have been as chaotic as previously thought, and raises many questions about how a well-ordered galaxy could have formed so soon after the Big Bang.

This ALMA finding follows the previous discovery announced in May of a rotating massive disk seen at a similar distance. Thanks to the lens effect, SPT0418-47 is seen in more detail and, in addition to a disk, it has a bulge, making it more like our current Milky Way than the galaxy previously studied.

Future studies, even with the Extremely Large Telescope ESO will try to find out just how typical these ‘baby’ disk galaxies really are and whether they are typically less chaotic than anticipated, opening up new avenues for astronomers to discover how galaxies evolved.

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