Milky Way galaxy is 'warped, twisted' not flat

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Cepheids pulse with a regular period that varies with their brightness. Image credit: Xiaodian Chen. These are young stars, between four and 20 times the mass of our sun and 100,000 times brighter.

The 1,339 stars are all Cepheid variables, a type of pulsating star whose intrinsic brightness depends on how long it takes to vary from bright to dim and back again. Until very recently, it has been very hard for scientists to visualize what the Milky Way looks like given that we are embedded inside it.

Without accurate measures of the distance between the sun and stars in the Milky Way's outer regions, it's hard to determine the precise shape of the galaxy and its gas disk.

In the centre, hundreds of billions of stars and dark matter hold the galaxy together.

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Combining their new results with those other observations, the researchers concluded that the Milky Way's warped spiral pattern is most likely caused by "torques"-or rotational forcing-by the massive inner disk".

"We used a new catalog of infrared observations obtained with the WISE space observatory to reduce the effects of dust and determine the distances to our Cepheids with uncertainties of less than 3 to 5 percent - that's an unprecedented accuracy to date", stated Richard de Grijs, an astrophysicist from Macquarie University and an author of the paper.

"It is notoriously hard to determine distances from the Sun to parts of the Milky Way's outer gas disk without having a clear idea of what that disk actually looks like", says Dr. Chen Xiaodian, a researcher at NAOC and lead author of the article published in Nature Astronomy.

Now the first accurate 3D map of its kind published in Nature Astronomy reveals they were right. Just like a goldfish can't see its bowl from the outside, our position in the universe means we can't see our home galaxy, the Milky Way, as the rest of the universe sees it.

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An artist's impression of the warped and twisted Milky Way disk.

Dr. Liu Chao, senior researcher and co-author of the paper said that the researchers observed other "warped" spiral galaxies.

"Perhaps more importantly, in the Milky Way's outer regions, we found the S-like stellar disc is warped in a progressively twisted spiral pattern". Researchers from the Macquarie University in Australia and the Chinese Academy of Sciences have found for the first time that our solar system is anything but stable and flat. In the galaxy's far outer disk, the hydrogen atoms making up most of the Milky Way's gas disk are no longer confined to a thin plane, but they give the disk an S-like warped appearance. So our Milky Way's twists are rare but not unique.

"This new finding may help us to know the shape of the Milky Way, and provide a key clue to understanding how galaxies such as the Milky Way form and evolve", said Deng Licai, co-author of the study.

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