Astronomers have discovered a distant galaxy, called SPT0418-47, that looks like a bright ring to our observatories. The effect is due to a process called gravitational lensing that distorts how the galaxy appears. In reality, the galaxy is remarkably similar to our own, the Milky Way – a surprise considering the light of this galaxy comes all the way from the early universe.
As reported in the journal Nature, we are seeing SPT0418-47 as it was 1.4 billion years after the Big Bang. This is a time when astronomers expect galaxies to still be chaotically forming, and yet this particular one sports two features similar to current galaxies: a rotating disk and a bulge.
SPT0418-47 doesn't have spiral arms like the Milky Way, but the presence of a disk places it with other recent discoveries of well-ordered galaxies from when the cosmos was still young. These findings don't sit well with theories of how galaxies formed.
“When I first saw the reconstructed image of SPT0418-47 I could not believe it: a treasure chest was opening,” lead author Francesca Rizzo, a graduate researcher from the Max Planck Institute for Astrophysics in Germany, said in a statement. “This result represents a breakthrough in the field of galaxy formation, showing that the structures that we observe in nearby spiral galaxies and in our Milky Way were already in place 12 billion years ago.”
Current telescopes are not powerful enough to study these galaxies without some help. That help comes in the form of a gravitational lens. Galaxies and galaxy clusters are massive enough to warp space-time, so with a serendipitous alignment, background distant galaxies can be magnified by the gravitational warp.
SPT0418-47 is perfectly aligned with the foreground galaxy in the observations conducted by the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA allowed the team to track the motion of the gas and understand the galaxy's true shape.
“What we found was quite puzzling; despite forming stars at a high rate, and therefore being the site of highly energetic processes, SPT0418-47 is the most well-ordered galaxy disc ever observed in the early Universe,” stated 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."
More observations and more galaxies need to be discovered from the early universe to deepen our understanding, and upcoming observatories like the European Southern Observatory’s Extremely Large Telescope are expected to do just that.