Astronomers have spotted a galaxy located 12 billion light years from Earth that unexpectedly looks like a younger version of our own galaxy, the Milky Way.
Because looking into the farthest reaches of the universe is also a way of looking back in time, the remote galaxy, called SPT0418-4, appears as it was in the early universe, just 1.4 billion years after the Big Bang.
Galaxies that formed in the universe’s turbulent childhood are expected to be chaotic tangles of stars and gas shaped by the disruptive growing pains of this early cosmic era. SPT0418-4, in contrast, is well-ordered and stable, which “demonstrates that at least some young galaxies are dynamically akin to those observed in the local universe, and only weakly affected by extreme physical processes,” according to a study published on Wednesday in Nature.
“It was a big surprise to find that this very young galaxy is quite similar to nearby spiral galaxies, contrary to all expectations from theoretical models and previous, less detailed observations,” said Francesca Rizzo, a PhD student at the Max Planck Institute for Astrophysics in Germany who led the research, in an email.
“On the other hand, when we started to work on SPT0418-47, we knew that there would be a high chance to observe something completely new, because we were looking, for the first time, at physical scales that have never been observed before at this cosmic time,” she added.
Galaxies like SPT0418-47 are normally too far-flung and faint to be studied in detail by astronomers. Fortunately, Rizzo and her colleagues got an assist from a type of natural cosmic telescope called a gravitational lens.
A large galaxy is aligned between Earth and SPT0418-47, and its gravitational field distorts and magnifies the light from the more distant galaxy, enabling Rizzo’s team to essentially zoom in on its finer properties.
“The magnifying power of gravitational lensing allowed us to observe a galaxy at the edge of the universe with the same precision that we can achieve for galaxies very close by,” Rizzo explained. “Imagine that you use a mobile phone with a camera from the 2000s and you take a picture of a distant object. Then you take the same picture with an iPhone 11. It would be like seeing the picture for the first time!”
The gravitationally lensed observations of SPT0418-47 were captured by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, which is currently the largest radio telescope in the world. The close-up views reveal that the galaxy has already evolved a stable rotating disk and a bulge of stars and gas around the galactic center, similar to many local spiral galaxies in our modern era, including the Milky Way.
That said, SPT0418-47 hasn’t sprouted the trademark helical arms of a spiral galaxy, and the team’s models suggest that it will more likely mature into an elliptical galaxy, a different type of structure than the Milky Way.
The sight of such a calm galaxy, in an era where pyrotechnic supernovas and frequent collisions are supposed to ruffle galactic feathers, challenges our understanding of how these massive structures coalesced and evolved in the early universe.
“The universe is dominated by so many complex phenomena that we do not yet have a comprehensive view of how galaxies are born and grow,” Rizzo said. “Although new insights have been achieved in the field of galaxy formation theory in the last years, the history of the young universe is one of the most outstanding puzzles of modern astrophysics.”
“For this reason, it is not trivial to find models of galaxy formation and evolution able to explain the characteristics of SPT0418-47,” she continued. “One of the ways to explain the characteristics of SPT0418-47 might be, therefore, to have a model for large-scale structure formation that will result in fewer collisions and mergers between young galaxies.”
Rizzo and her colleagues plan to continue scanning these distant vistas, with the aim of understanding whether SPT0418-47 is an outlier, or one of many stable galaxies chilling out in the universe's early days.