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Astronomers reveal a twisted and twisted Milky Way



The Milky Way in a turn

The artistic impression of the twisted and twisted disk of the Milky Way. (Image of CHEN Xiaodian)

The star disk of our Milky Way galaxy is anything but stable and flat. Instead, it becomes increasingly "warped" and twisted away from the center of the Milky Way, according to astronomers at the National Astronomy Observatories of the Chinese Academy of Sciences (NAOC).

From a great distance, our galaxy would look like a thin disk of stars that orbit once every few hundred million years around its central region, where hundreds of billions of stars, along with a large mass of dark matter, they provide the "glue" gravitational. to keep everything together.

But the force of gravity weakens away from the inner regions of the Milky Way. In the far outer disk of the galaxy, the hydrogen atoms that make up most of the Milky Way's gas disk are no longer confined to a thin plane, but give the disk a distorted S-shape.

"It is notoriously difficult to determine the distances from the Sun to parts of the outer gas disk of the Milky Way without having a clear idea of ​​how that disk actually looks," says Dr. Chen Xiaodian, NAOC researcher and lead author of the article. . Published in Nature Astronomy.

Milky Way Twisted

Above: Three-dimensional distribution of classical Cepheid variable stars in the warped disk of the Milky Way (red and blue dots) centered on the location of the Sun (large orange symbol). Astronomers use the units & # 39; kpc & # 39; (kiloparsecs) along the three axes of the image to indicate the distances at scales of the entire galaxy. One kiloparsec is equivalent to about 3,262 light years. Inferior: Precession of the line of warp nodes with galactocentric radius. (Image of CHEN Xiaodian)

"However, we recently published a new catalog of well-behaved variable stars known as classic Cepheids, for which you can determine such precise distances from 3 to 5%." That database allowed the team to develop the first accurate three-dimensional image of our Milky Way to its most remote regions.

Classical Cepheids are young stars that are four to 20 times more massive than our Sun and up to 100,000 times brighter. Such high stellar masses imply that they live fast and die young, burning their nuclear fuel very quickly, sometimes in only a few million years. They show pulsations from one day to the next, which are observed as changes in their brightness. Combined with the observed brightness of a Cepheid, its pulsation period can be used to obtain a highly reliable distance.

"To our surprise, we found that in 3D our collection of 1339 Cepheid stars and the gas disk of the Milky Way are closely watched. This offers new insights into the formation of our domestic galaxy, "says Prof. Richard de Grijs of Macquarie University in Sydney, Australia, and co-lead author of the article." Perhaps most importantly, in the outer regions of the Milky Way, we found that the S-type stellar disc is deformed in a progressively twisted spiral pattern. "

This reminded the team of the previous observations of a dozen other galaxies that also showed progressively twisted spiral patterns. "Combining our results with these other observations, we conclude that the deformed spiral pattern of the Milky Way is probably caused by" torques "- or rotational forcing – by the massive internal disk," says Dr. LIU Chao, principal investigator and co-author of the paper.

"This new morphology provides a crucial updated map for studies of the stellar motions of our galaxy and the origins of the Milky Way disk," says Dr. DENG Licai, NAOC principal investigator and co-author of the article.

Publication: Xiaodian Chen, et al., "An intuitive 3D map of the precession of the galactic warp traced by the classic Cepheids," Nature Astronomy (2019)


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