The star disk of our Milky Way is anything but stable and flat. Instead, it becomes increasingly "distorted" and twisted away from the center of the Milky Way, according to astronomers at Macquarie University and the Chinese Academy of Sciences who built the first accurate 3D map of the Earth's galaxy and revealed it today in a newspaper. published in Astronomy of Nature.
From a great distance, our galaxy would look like a thin disk of stars that orbit once every few hundred million years around its central region, where hundreds of billions of stars provide the gravitational "glue" to hold them together.
But the force of gravity becomes weaker away from the inner regions of the Milky Way. In the outermost disk of the galaxy, the hydrogen atoms that make up most of the Milky Way gas disc are no longer confined to a rarefied plane, but give the disk a distorted S-shaped appearance.
"It is notoriously difficult to determine distances from the sun to parts of the external gas disc of the Milky Way without having a clear idea of what this disk really is," says Xiaodian Chen, a researcher at the Chinese Academy of Sciences in Beijing and the lead author of the article in Astronomy of Nature.
"However, we have recently published a new catalog of well-behaved variable stars known as classic Cepheids, for which distances as accurate as 3 to 5 percent can be determined." This database allowed the team to develop the first accurate three-dimensional image. from our Milky Way to its most distant regions.
Classic Cepheids are young stars that are four to 20 times as massive as our Sun and up to 100,000 times brighter. These high stellar masses imply that they live fast and die young, burning their nuclear fuel very quickly, sometimes in just a few million years.
They show pulsations from one day to the next, which are observed as changes in their brightness. Combined with the observed brightness of Cepheid, your heartbeat period can be used to achieve a highly reliable distance.
"To our surprise, we discovered that in 3D our collection of 1339 stars Cepheid and the Milky Way gas disc follow. This offers new insights into the formation of our home galaxy, "says Professor Richard de Grijs of Macquarie University, an astronomer and senior co-author of the study.
"Perhaps more importantly, in the outer regions of the Milky Way, we find that the S-type star disk is deformed into a progressively twisted spiral pattern."
This reminded the team of previous observations of a dozen other galaxies that also showed progressively distorted spiral patterns.
Combining their new findings with the other observations, the researchers concluded that the distorted spiral pattern of the Milky Way is probably caused by "torques" – or rotational forcing – by the huge inner disk.
"This new morphology provides an updated map crucial for studies of our galaxy's stellar motions and the origins of the Milky Way's disk," according to Licai Deng, a senior researcher at the Chinese Academy of Sciences and co-author of the paper.