Extremely distant, infant galaxy looks surprisingly like our own Milky Way

13 Aug 2020

A reconstruction of galaxy SPT0418-47’s true shape. Image: ALMA (ESO/NAOJ/NRAO), Rizzo et al

Astronomers have spotted the faint glimmer of a distant galaxy that is not only surprisingly stable, but very like our own Milky Way.

Researchers have described a recent discovery as a “breakthrough in the field of galaxy formation”, with help from the Atacama Large Millimeter/submillimeter Array (ALMA). Writing in Nature, astronomers revealed images of a very young galaxy, which is so far away that light has taken 12bn years to reach us.

This means we are seeing the galaxy, dubbed SPT0418-47, as it was when it was just 1.4bn years old. What really surprised the researchers was that while it doesn’t appear to have spiral arms, this galaxy does have at least two features similar to our own Milky Way.

This includes a rotating disc and a bulge containing a large group of stars packed tightly around the galactic centre. 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 look-alike.

“The big surprise was to find that this galaxy is actually quite similar to nearby galaxies, contrary to all expectations from the models and previous, less detailed, observations,” said co-author Filippo Fraternali from the University of Groningen in the Netherlands.

Like a ‘treasure chest’ opening

While detailed observations of such distant galaxies are impossible with even the most powerful telescopes, the astronomers used gravitational lensing to see SPT0418-47 by using a nearby galaxy as a powerful magnifying glass. With this effect, the gravitational pull from the nearby galaxy distorts and bends the light from the distant galaxy, causing it to appear misshapen and magnified.

Appearing as a near-perfect ring of light around the nearby galaxy, the researchers were then able to reconstruct the galaxy’s true shape and the motion of its gas from the ALMA data using a new computer modelling technique.

Francesca Rizzo, a PhD student from the Max Planck Institute for Astrophysics who led the study, said seeing the reconstructed image for the first time was like a “treasure chest” opening.

Even more surprising to the researchers was the fact that the galaxy appears to be the most well-ordered galaxy disc ever observed in the early universe. However, it’s expected it will eventually evolve into a galaxy very different from the Milky Way and join the class of elliptical galaxies that inhabit the universe today.

This unexpected discovery suggests the early universe may not be as chaotic as once believed and raises many questions on how a well-ordered galaxy could have formed so soon after the Big Bang.

Colm Gorey was a senior journalist with Silicon Republic