- Researchers create a precise 3D map of the Milky Way out to its far outer zones.
- The new map shows that the S-shaped disc of stars becomes progressively warped and twisted the further away the stars are from the center of the Milky Way.
We don’t know the shape of our galaxy particularly well, that’s for sure. And since we are sitting within the Milky Way, we do not have any specific vantage point to see the rest of our Galaxy.
In recent decades, scientists have made great strides in determining the appearance of Milky Way but it is still pretty fuzzily mapped. So far, we have learned one thing for sure: Milky Way’s disk of stars isn’t flat and stable.
Now, a team of researchers at Chinese Academy of Sciences have revealed that the disk of our galaxy becomes more warped and twisted as you go farther away from the center of the Milky Way.
Observing Our Galaxy From a Great Distance
For someone who is sitting billions of light years away, Milky Way would look like a slim disk of stars orbiting around its central core once every several hundred million years. This disk contains about 100 billion stars and a massive amount of dark matter that holds everything together.
However, the pull of gravity is much stronger in the galaxy’s core compared to its outer regions. As per the published paper, in the far outer disk of Milky Way, the atoms (especially hydrogen atoms that make up most of the galaxy’s gas) are no longer enclosed in a thin dimension. Instead, they are arranged in a way that gives the disk a curious S-shape appearance.
Artistic impression of the warped and twisted disk of our galaxy | Credit: CHEN Xiaodian
Without knowing what actually our galaxy’s outer gas disk looks like, astronomers cannot determine distances from the Earth to other distant stars in the galaxy’s outer regions.
In this study, researchers built a new catalogue of Cepheids (a special class of stars) for which distances can be evaluated with an accuracy of 3 to 5 percent. Using this catalogue, they were able to create a precise 3D map of the Milky Way out to its far outer zones.
What Exactly Are Cepheids?
Classical Cepheids are stars that dim and brighten periodically. Due to this behavior, astronomers can use them as comic yardsticks out to distances of several millions of light-years. These young stars can be 4 to 20 times more massive and 100,000 times brighter than our Sun. They burn their nuclear fuel in just a few million years.
3D map of the Milky Way’s disk traced by Cepheids | Courtesy of researchers
In the new catalogue, researchers discovered that the Milky Way’s gas disk and 1,339 Cepheids follow each other closely. This data allowed them to see the formation of our galaxy from a whole new perspective. They discovered that the S-shaped disc of stars becomes progressively warped and twisted the further away the stars are from the center of the Milky Way.
Such increasingly twisted spiral patterns have already been observed in other galaxies. Researchers combined their outcome with those observations and deduced that this warped spiral pattern is caused by rotational forces (torques) induced by Milky Way’s massive inner disk.
Overall, this morphology offers an updated map for studies of the archaeology and kinematics of the Galactic Disk. Further observations, such as ESA’s Gaia mission, will release more precise catalogue (in 2022), revealing more secrets of our galaxy.