A few hundred billion suns circle in our Milky Way. At its center lies a black hole whose gravitational effect holds the whole galaxy together. And from a distance, it looks like the stars are rotating in a flat disk around the center. But if you got closer, the picture would change - because in truth, this disc is not flat at all.
On the outskirts of the Milky Way, the galactic disc is bent up on one side and down on the other side. This is the conclusion of a Chinese-Australian research team led by Chen Xiaodian of the Chinese Academy of Sciences in Beijing, who has just presented his findings in the journal Nature Astronomy.
The scientists had determined the exact positions of 1339 special stars. These belong to the group of Cepheids, which are also called cosmic milestones. They shine up to 100,000 times brighter than our sun and can therefore be seen over long distances. Their brightness fluctuates in a regular cycle, the length of which depends on the luminosity of the respective star.
Torque of the rotating massive star disk
From this, their distance can be determined very well: Due to the fluctuation rhythm, the astronomers know the absolute brightness of a Cepheid star and can calculate how far away he must be, so that he appears just as bright in the earthly firmament as observed. In this way, the scientists of each Cepheid studied not only the exact position in the sky, but also its exact distance - the result is a three-dimensional map.
Macquarie University
Researcher de Grijs: Search for the shape of the Milky Way
"We usually think of spiral galaxies as relatively flat," says co-author Richard de Grijs of Macquarie University in Sydney. The map shows, however, that the disc is warped and twisted. As a cause, the astronomers suspect a torque of the rotating massive inner star disk of the Milky Way.
Such a warped spiral has been observed in about a dozen other galaxies, the researchers explain. The shape of our Milky Way is therefore rare, but not unique.