Our universe is 13.8 billion years old . Now, the ALMA observatory, located in the Atacama desert (Chile), has discovered a galaxy like ours, which formed 1.5 billion years after the Big Bang, when the universe was still very young. It is the most distant galaxy ever detected.
Rotating disk galaxies, such as the Milky Way, are common throughout the universe, but no one as large and as old as this one, named DLA0817g , has never been discovered, since the universe was 10% as old as it is now.
The oldest disc-shaped galaxy ever seen
His disc, dubbed the Wolfe Disc in honor of the astronomer Arthur M. Wolfe (who died in 2014 of cancer), renowned for his discoveries about star formation and the early universe, rotates at 272 kilometers per second and weighs 72,000 million times the mass of the Sun. Observations, made by the Atacama Large Millimeter / submillimeter Array (ALMA), contradict traditional models in which a massive disk galaxy like DLA0817g would be expected to eventually form around 6 billion years after the Earth. Big Bang, but not as soon as this.
“While previous studies hinted at the existence of these first rotating gas-rich disk galaxies, thanks to ALMA we now have unequivocal evidence that they occur as early as 1.5 billion years after the Big Bang,” commented Marcel Neeleman of Max Planck. Institute of Astronomy, leader of the study published in the journal Nature.
Although the galactic disk rotates at a speed similar to that of the Milky Way, “the rate of star formation in the Wolfe disk is at least 10 times higher than in our own galaxy,” said J. Xavier Prochaska, an astronomer at the University from California in Santa Cruz and also a co-author of the work. “It must be one of the most productive disk galaxies in the early universe.”
Challenging the paradigm
The fact that this galaxy formed just 1.5 billion years after the Big Bang suggests that massive spiral galaxies like the Milky Way can grow relatively fast, as previous observations showed that disk-shaped galaxies, including spiral systems in expansion like the Milky Way, did not appear in large numbers until between 3,000 and 4,000 million years after the Big Bang, which took place about 13.8 billion years ago.
Galaxies are believed to form through many smaller galaxy mergers, as well as through the capture of hot clumps of gas. The process is chaotic and leads to a disorderly galaxy that only becomes a quieter and more orderly object after billions of years. Clearly, another mechanism is necessary to explain the Wolfe Disk . Then?
Cold accretion method
“We believe that the Wolfe Disc has grown primarily through the constant build-up of cold gas ,” added Prochaska. “Still, one of the questions that remains is how to assemble such a large mass of gas while maintaining a relatively stable spinning disk.”
The galaxy was first discovered in 2017 while the team was studying light from a distant luminous quasar, a particular type of active galaxy. The quasar’s emission was altered by the large hydrogen cloud surrounding the Wolfe Disk, allowing the discovery of a much fainter galaxy.
“The fact that we found the Wolfe disk using this method tells us that it belongs to the normal population of galaxies present in the early cosmos,” Neeleman said. “When our most recent observations with ALMA showed that it was spinning, we realized that the first spinning disk galaxies are not as rare as we thought and that there should be many more .”
Referencia: A cold, massive, rotating disk galaxy 1.5 billion years after the Big Bang, Nature (2020). DOI: 10.1038/s41586-020-2276-y , www.nature.com/articles/s41586-020-2276-y
