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The ALMA telescope in Chile has helped a team of astronomers to observe a very distant galaxy that is surprisingly similar to the Milky Way.
It is SPT0418-47 and its distorted light, observed thanks to a gravitational lens or ‘magnifying glass effect’ from another nearby galaxy, has taken 12 billion years to reach Earth.
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 theAtacama 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 slowmore than 12 billion years to get to 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, a doctoral student at the Max Planck Institute for Astrophysics in Germany, who led the research published today inNature.
Although the galaxy studied, calledSPT0418-47, 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 ever observed.
"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 suggestsFilippo 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 located, 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 asgravitational 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 near 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-authorSimona 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 characteristics 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 theExtremely Large Telescope ESO, will try to discover how typical these 'baby' disk galaxies really are and whether they are less chaotic than expected, opening up new avenues for astronomers to discover how galaxies evolved.