ALMA detects a distant galaxy similar to the Milky Way
Astronomers using the Atacama Large Milimiter / sublimiter Array ALMA, in which the European Southern Observatory ESO is a partner, have revealed an extremely distant and therefore very young galaxy that resembles our Milky Way. The galaxy is so far away that its light has taken more than 1.20 * 10^10 years to reach us: we see it as it was when the Universe was only 1.40 * 10^9 million years old. It is also surprisingly slightly chaotic, as it contradicts theories that all galaxies in the early Universe were turbulent and unstable. This unexpected discovery challenges our understanding of how galaxies form, providing insight into the past of our Universe.
“This result represents a breakthrough in the field of galaxy formation, showing that the structures we observe in nearby spiral galaxies and in our Milky Way were in place 12 * 10^9 years ago,” says Francesca Rizzo, PhD student at the Max Planck Institute for Astrophysics in Germany, who led the research published in Nature. While the galaxy that astronomers studied, called SPT0417–47, does not appear to have spiral arms, it does have at least two features of our Milky Way: a spinning disk and a bulge, the large cluster of stars packed tightly around the galaxy. 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.
“The big surprise was to find that this galaxy is actually quite similar to nearby galaxies, contrary to all previous, less detailed expectations,” 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 formation, so the researchers expected them to be chaotic and lacking the distinctive structures typical of more mature galaxies like the Milky Way.
Galaxy SPT0418–47 is gravitationally reflected by a nearby galaxy, which appears in the sky as an almost perfect ring of light. The research team reconstructed the actual shape of the distant galaxy and the motion of its gas from the ALMA data using a new computer modeling technique. Observations indicate that SPT0418–47 is a disk galaxy with a central bulge and the material that revolves around the center.
Gas moving away from us is shown in red, while gas moving towards the observer is shown in blue.
The study of distant galaxies like SPT0418–47 is essential to understand how galaxies formed and evolved. This galaxy is so far away that we see it when the Universe was only 10% of its current age, when studying it we go back to a time when these baby galaxies were just beginning to develop.
Because these galaxies are so far away, detailed observations even with the most powerful telescopes are nearly impossible, as the galaxies appear small and faint. The team overcame this hurdle using a nearby galaxy as a powerful magnifying glass, an effect known as gravitational lensing, 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, making it appear warped and magnified.
The distant, gravitationally lensed galaxy appears as a nearly perfect ring of light around the nearby galaxy, thanks to its near-exact alignment. The research team reconstructed the actual 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.
“What we found was quite puzzling; despite stars forming at a high rate and therefore the site of highly energetic processes, SPT0418–47 is the best-ordered disk of galaxies ever observed in the early Universe.” said 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.” 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 of elliptical galaxies. , another type of galaxies that, together with spirals, inhabit the Universe today.
This unexpected discovery suggests that the early Universe may not be 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 find follows the previous discovery announced in May of a huge spinning disk seen at a similar distance. SPT0418–47 is seen in more detail, thanks to the lens effect, and has a bulge in addition to a disk, which makes it even more similar to our current Milky Way than the one studied previously.
Future studies, including ESO’s Extremely Large Telescope, will seek to discover how typical these “baby” disk galaxies really are and if they are commonly less chaotic than anticipated, opening up new avenues for astronomers to discover how galaxies evolved.
