An international team of astronomers has observed the most ancient spiral galaxy yet, which formed when the universe was 2.6 billion years old, about one-fifth of its current age.
The object known as A1689B11 is a remarkable find. As the team explains in their research paper, which will be published in the Astrophysical Journal, this is only the second spiral which has been observed further than 10 billion years from Earth. These observations are the first step in understanding how spiral galaxies, like the Milky Way, came to form and importantly what they looked like at the beginning.
"This galaxy is forming stars 20 times faster than galaxies today – as fast as other young galaxies of similar masses in the early universe. However, unlike other galaxies of the same epoch, A1689B11 has a very cool and thin disc, rotating calmly with surprisingly little turbulence. This type of spiral galaxy has never been seen before at this early epoch of the universe," lead author Dr Tiantian Yuan from Swinburne University of Technology in Australia, said in a statement.
Galaxies are believed to have formed in the gravitational space-time depression created by dark matter. Hydrogen gas flowed inside them in the first few million years after the Big Bang, where it collapsed into stars and eventually supermassive black holes. Over billions of years, these proto-galaxies became spirals although the exact sequence of events is not yet clear.
"Spiral galaxies are exceptionally rare in the early universe, and this discovery opens the door to investigating how galaxies transition from highly chaotic, turbulent discs to tranquil, thin discs like those of our own Milky Way galaxy."
The observations were possible using a gravitational lens. Massive objects, in this case, a cluster of galaxies, can bend space-time in a way that the source of light behind them is magnified as if it is going through a lens. The light from A1689B11 experienced just that, so the team was able to see it.
"This technique allows us to study ancient galaxies in high resolution with unprecedented detail," added Dr Yuan. "We are able to look 11 billion years back in time and directly witness the formation of the first, primitive spiral arms of a galaxy."
More galaxies like A1689B11 are likely to exist and we'll soon be able to find them. When telescopes like the James Webb Space Telescope come online in a few years, we’ll see more of these objects and in better detail.
