Bent spiral: the 3D map shows the shape of the Milky Way

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<p class=Our Milky Way – a folded spiral.

Chao Liu (National Astronomical Observatories, Chinese Academy of Sciences) / dpa

A Sino-Australian research group determined the exact positions of hundreds of special stars and used them to create a three-dimensional map. This shows: The Milky Way is a spiral galaxy. Apparently also a special one.

The Milky Way has the shape of a bent spiral. This shows a detailed three-dimensional map of our domestic galaxy. On the periphery its galactic disk is bent upward on one side and down on the other side. A Chinese-Australian research group led by Chen Xiaodian from the Chinese Academy of Sciences in Beijing presented the map in the journal Nature Astronomy.

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<p class=3D distribution of Cepheids in the twisted disc of the Milky Way.

(Photo: Chen Xiaodian / dpa)

The scientists had determined the exact positions of 1339 special stars. The stars studied belong to the group of Cepheids (pronounced Ke-feh-iden), which are also called cosmic milestones. These stars 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, whose length depends on the brightness of the respective star.

From this, their distance can be determined very well: because of the fluctuation rhythm, astronomers know the absolute brightness of a Cepheid star and can calculate how far it must be, so that it appears equally 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.

Rarely, but not unique

"We usually think that spiral galaxies are relatively flat," said co-author Richard de Grijs of Macquarie University in Sydney in a statement released by his college. The map shows, however, that the disk is deformed and distorted. As a cause, astronomers suspect a pair of the massive rotating inner stellar disk of the Milky Way.

A spiral that has been deformed has been observed in about a dozen other galaxies, the researchers explain. The shape of our Milky Way is therefore rare, but not unique.

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