A team of astronomers announces that they have identified the oldest known spiral galaxy in the universe, formed around 12.4 billion years ago. This work could allow us to learn more about the origin and fate of our own galaxy. Details of the study are published in the journal Science.
There are three main types of galaxies in the universe:ellipticals, irregulars and spirals. The former are spheroidal concentrations of billions of stars that look like huge globular clusters. Seconds are, as their name suggests, objects that display no regular or discernible structure. Finally, the spirals feature distinct internal structures, including a stellar bulge, disc, and arms. Our galaxy, the Milky Way, belongs to this category.
It is still unknown when the first spiral galaxies formed, but a new discovery reduces the uncertainties. The object, named BRI 1335-0417, would indeed have formed about 1.4 billion years after the Big Bang , making it the oldest known example of this type of galaxy. The oldest known galaxy of any category remains GN-z11, an irregular object formed about 400 million years after the Big Bang.
BRI 1335-0417 was discovered somewhat by chance by Takafumi Tsukui, from SOKENDAI University of Advanced Studies in Japan, after finding a photo of it in the archives of the Atacama Large Millimeter/Submillimeter Antenna Array (ALMA). To an untrained eye, the image might appear blurry. In fact, it offers many details for such a distant galaxy.
"I was excited because I had never seen such clear evidence of a spinning disk, a spiral structure, and a structure centralized mass in a distant galaxy in any prior literature “, explains the researcher. "The quality of the ALMA data was so good and the detail so extensive that I first thought it was a nearby galaxy “.
This spiral galaxy is surprisingly large for its time, measuring 15,000 light-years in diameter , about one-third the size of the Milky Way. It is also very dense, containing about the same amount of mass than our galaxy. To explain it, the authors suggest that the object could have formed from a violent collision between two smaller galaxies.
The eventual fate of BRI 1335-0417 could also provide exciting clues about the future of spiral galaxies which make up about 72% of the observable galaxies in the universe . Some believe that spirals are precursors to elliptical galaxies, but how this transformation occurs remains a mystery.
Naturally, these works also refer us to our own galaxy. “Our solar system is located in one of the spiral arms of the Milky Way “, recalls indeed Satoru Iguchi, of the National Astronomical Observatory of Japan and co-author of the study. "Tracing the roots of the spiral structure will give us clues to the environment in which the Solar System was born “.
