The stellar disk of our Milky Way Galaxy is completely unstable, far from flat, and it is becoming more twisted and bent away from the center.
From a long distance, a significant part of our galaxy would look like a thin disk of stars that for several hundred million years make one revolution around the central region, where hundreds of billions of luminaries, together with a huge mass of dark matter, provide the gravitational glue that holds the galactic mass.
But gravity weakens away from the internal regions of the Milky Way and the hydrogen atoms in the outer disk of the Galaxy, which make up most of it, are no longer limited to a thin plane and give it an S-shaped curved appearance.
It’s common knowledge that it’s difficult to determine the distance from the Sun to the outer gas disk of the Milky Way without having a clear idea of how it actually looks.
-Dr. Xiaodian Cheng, lead author of the study from the National Astronomical Observatory of the Academy of Sciences of China
Using a recently published catalog of variable stars, known as classic Cepheids, the distance to which can be determined with an error of only 3-5%, the team developed the first accurate three-dimensional map of remote areas of the Milky Way.
Classic Cepheids are young stars that are 4 to 20 times more massive than the Sun and 100,000 times brighter. High stellar masses mean that they live fast and die young, burning their nuclear fuel for several million years. They show pulsations with a periodicity from day to month, which manifest themselves in a change in their brightness. In combination with the observed luminosity, the pulsation period is used to obtain a very accurate distance.
To our surprise, we found that in the resulting 3D collection of 1339 cepheids, the stars and the gas disk of the Milky Way closely follow each other. This gives a new insight into the formation of our galaxy. However, in our opinion, more importantly, in the outer areas of the Milky Way, the S-shaped star disk is twisted into a gradually twisting spiral structure.
-Richard de Griss, co-author of the study from Macquarie University in Sydney (Australia)
The discovery reminded the team of earlier observations of a dozen other galaxies, which also showed similar structures. Astronomers have come to the conclusion that the curvature of our Galaxy is most likely caused by the “torque” of its massive internal disk.
A new morphology gives us an important updated picture of our Galaxy to study the movement of the luminaries and the origin of the Milky Way disk.
-Litsai Dan, co-author of the study from the National Astronomical Observatory of the Chinese Academy of Sciences
The Milky Way's stellar disk is unstable and significantly curved
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