Researchers probing the distant reaches of space have found an ancient galaxy with spiral arms just like our own, the Milky Way.
At 12.4 billion years old, the spiral galaxy, named BRI 1335-0417, is the oldest ever discovered.
Galaxies of this shape are thought to make up 70% of the ones in the universe. But they seem to become rarer the further back in history you look.
Finding one of this age and shape was a big surprise for the research team, who made the discovery while combing through data from the ALMA (Atacama Large Millimeter Array) radio telescope.
Lead study author Takafumi Tsukui said: ‘I was excited because I had never seen such clear evidence of a rotating disc, spiral structure, and centralised mass structure in a distant galaxy in any previous literature.
‘The quality of the ALMA data was so good that I was able to see so much detail that I thought it was a nearby galaxy.’
The galaxy, which existed just 1.4 billion years after the Big Bang, is about a third of the size of the Milky Way. That’s ‘giant’ for an ancient galaxy, Tsukai added.
Scientists don’t know how a galaxy of this shape developed so early on, but they think it might be the result of a collision with another, smaller galaxy.
It’s thought that spiral structures can form when small galaxies smash into each other and merge into larger galaxies. The video above is a computer simulation of this kind of formation.
These collisions can bring large amounts of gravitationally unstable gas to a galaxy, providing good conditions for stars to form.
BRI 1335-0417 has this kind of unstable gas in its outer region, and it’s actively producing stars.
Many more mysteries about this ancient galaxy remain. Scientists don’t know, for example, if its structure will change over time.
Ancient dust-rich, star-forming galaxies are thought to be the predecessors of giant elliptical galaxies in the present universe.
If it follows this pattern, BRI 1335-0417 will morph from a disc galaxy to an elliptical galaxy. Alternatively, it might retain its spiral structure.
Whatever happens to it, the team say it will shed light on scientists’ understanding of galactic structures.
Researcher Satoru Iguchi said: ‘Our Solar System is located in one of the spiral arms of the Milky Way.
‘Tracing the roots of spiral structure will provide us with clues to the environment in which the Solar System was born. I hope that this research will further advance our understanding of the formation history of galaxies.’
The research was published Thursday in the journal Science.