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The Milky Way’s shape — a peculiar disk

Popular media is abuzz today with news regarding research by NAOC (National Astronomical Observatories of Chinese Academy of Sciences) on the shape of our galaxy, the Milky Way, published in Nature Astronomy today. A peculiar disk. A new 3D model.

Original article on Nature Astronomy: “An intuitive 3D map of the Galactic warp’s precession traced by classical Cepheids” (February 4, 2019).

Here’re two examples about that article: ABC Science News and The article contains visualizations.

Milky Way is ‘S-shaped’, 3D map reveals, in a new way of looking at our celestial home

Key points:

  • We have long thought the Milky Way was warped, but it is also twisted, according to a new study of pulsating stars.
  • The new map is the most accurate representation of the Milky Way so far, say astronomers.
  • The Gaia telescope will give us a much better picture in the future.

The map provides an “unprecedented view of the Milky Way”, said study co-author Richard de Grijs of Macquarie University.

To create the map, Professor de Grijs and colleagues from the Chinese Academy of Sciences focused on 1,339 pulsating beacons known as Cepheid stars.

To cut through the dust, Professor de Grijs and colleagues based their calculations on observations of Cepheid stars made using the Wide-Field Infrared Survey Explorer, which detects longer wavelengths than visible light.

Joss Bland-Hawthorn of the University of Sydney agreed the new study was a first step, which will be followed up in more detail by observatories such as the Gaia space telescope.

“This is probably the cleanest demonstration of the warp in stars and it looks different from the warp in gas,” said Professor Bland-Hawthorn, who was also not involved in the new study.

But we don’t really know what causes these warps, he added.

The Milky Way is warped

The Milky Way galaxy’s disk of stars is anything but stable and flat. Instead, it becomes increasingly warped and twisted far away from the Milky Way’s center, according to astronomers from National Astronomical Observatories of Chinese Academy of Sciences (NAOC).

“Somewhat to our surprise, we found that in 3-D, our collection of 1339 Cepheid stars and the Milky Way’s gas disk follow each other closely. This offers new insights into the formation of our home galaxy,” says Prof. Richard de Grijs from Macquarie University in Sydney, Australia, and senior co-author of the paper. “Perhaps more importantly, in the Milky Way’s outer regions, we found that the S-like stellar disk is warped in a progressively twisted spiral pattern.”

“This new morphology provides a crucial updated map for studies of our galaxy’s stellar motions and the origins of the Milky Way’s disk,” says Dr. DENG Licai, senior researcher at NAOC and co-author of the paper.

We’ve come a long way from “perfect” celestial spheres, eh.