The Milky Way was curved

Our galaxy is not a flat, but a curved disk. In profile, it is somewhat reminiscent of the letter S.

Such conclusions are made in a study published by scientists from China in the journal Nature Astronomy.

By itself, this idea is not new. Back in 2006, radio astronomers expressed it based on observations of interstellar hydrogen. However, many experts have questioned this result. In such observations, it is difficult to determine the exact distances to different parts of the gaseous disk, which means that it becomes problematic to talk about its geometry.

The new study is based on one of the most reliable “dimensional lines” in astronomy. This is a classic Cepheid.

These are young stars that are 4–20 times as massive as the Sun and tens and hundreds of thousands of times brighter than it. A characteristic feature of Cepheids is a periodic change in radius. The star shrinks and opens with a period of several days, weeks, or months.

For Cepheids, a fairly accurate relationship was established between the pulsation period and the luminosity. Therefore, knowing this period, it is possible to calculate the energy release of the star. Comparing it with the visible brilliance, you can determine the distance to the star. The error of such a “line” is 3-5%.

The authors determined the distances to 1339 Cepheids located in different parts of the Milky Way disk.

“To our surprise, we found that in three-dimensional space our set of 1339 Cepheids and the gas disk of the Milky Way are very close to each other. This gives a new idea about the formation of our galaxy,” admits study co-author Richard de Grijs. from China Western Pedagogical University.

The curvature of the stellar disk is almost imperceptible in the center, but increases towards the edges.


The geometry of the Milky Way according to researchers.
Illustration by Chen Xiaodian.

The picture obtained by astronomers is shown in the figure. At the top is a three-dimensional map of the distribution of Cepheids (red and blue dots). The sun is shown by a large orange ball. Below, the angle of deviation of the disk from the plane, depending on the distance to the center of the Galaxy. Note that on average, this angle was equal to 17.5 °.

Similar S-shaped galaxies are already known to astronomers. Experts believe that the edges of the disk bend under the action of the moment of force from its massive internal part.