Milky Way is warped and twisted, not flat

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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. The energetic stars pulsate, and by messing the timing of the stellar pulses and the changes in brightness, scientists can accurately measure their distance from Earth and the sun. Classical Cepheids are 20 times more massive that the sun and as much as 100,000 times brighter. "We usually think of spiral galaxies as being quite flat, like Andromeda which you can easily see through a telescope", says Professor Richard de Grijs, a co-author and astronomer from Australia's Macquarie University. So our Milky Way's twists are rare but not unique, the astronomers added.

"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", said Chen Xiaodian, lead author of the paper.

Previously, astronomers saw evidence of hydrogen clouds becoming warped in the Milky Way. The outer reaches of the galaxy are hard to image, given that the Milky Way is 100,000 light-years, or 0.5 quintillion miles (1 quintillion kilometers), across.

Top: Three-dimensional distribution of the classical Cepheid variable stars in the Milky Way's warped disk (red and blue points) centered on the location of the Sun ( large orange symbol).

Astronomers have observed a dozen other galaxies which showed similar progressively twisted spiral patterns in their outer regions.

Given their mass and brightness, they probably burn through their fuel quickly and die after a few million years - young for the lifetime of a star. We know the Milky Way is a spiral galaxy - a thin disk of a hundred billion stars that circle around a huge supermassive black hole at the galaxy's centre. The new study found that the farther away you travel from the galactic core, this disk becomes increasingly warped and twisted.

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"Somewhat to our surprise, we found that in 3D our collection of 1339 Cepheid stars and the Milky Way's gas disk follow each other closely".

The pull becomes weaker away from the inner regions. Since hydrogen atoms in the far outer disk are no longer confined to a thin plane, they get warped.

"We would need to do (numerical) simulations of a realistic galaxy embedded in a dark matter halo to see if we can reproduce the observations and figure out how this came about", says de Grijs.

Researchers from Macquarie University, Australia, and the Chinese Academy of Sciences made their findings after creating a new 3-D map of the Milky Way, which allowed them to better estimate its shape. That's according to a new study of 1,339 stars whose distances could be measured with great accuracy.

The team had published the results of their work in the Nature Astronomy, saying that their map will be "crucial" in further studies of the kinematics and archaeology of our galaxy.

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