Galactic Twist: The Warped Shape of Our Milky Way's Disk

Mindy Sparks
February 6, 2019

The shape of the Milky Way, usually pictured as a flat spiral, may actually be more like a warped and twisted disk.

The Milky Way turned out to be progressively twisted in its outer areas, which is most likely caused by the powerful rotating forces released by the galaxy's massive internal disk, according to the research.

It turns out that the further the stars are from the center of the galaxy, the weaker their gravitational pull is.

"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 Chinese Academy of Sciences astronomer Dr. Xiaodian Chen, lead author of the study.

A new analysis of pulsing stars has revealed the Milky Way's twisted shape. 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.

Because they are so bright, Cepheids can be clearly seen millions of light years away and can be easily distinguished from other bright stars in their vicinity, making them indispensable tools in any astronomers' kit. Astronomers from Macquarie University and the Chinese Academy of Sciences have used 1339 "standard" stars to map the real shape of our home galaxy in a paper published in Nature Astronomy today.

The new stellar distance database allowed scientists to build a detailed 3D map of the Milky Way's gas disk.

The researchers gathered 2,330 Cepheid variables catalogued by an infrared telescope called the Wide-field Infrared Survey Explorer, and whittled down the list to 1,339 stars based on their distance, models of the Milky Way, and other factors. These are young stars, between four and 20 times the mass of our sun and 100,000 times brighter.

"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", said Licai Deng, senior researcher at the Chinese Academy of Sciences. They also pulsate radially for days to months at a time - and this period of pulsation can be combined with the Cepheid's brightness to reliably establish its distance from the sun. "This offers new insights into the formation of our home galaxy", Richard de Grijs, senior study co-author and professor at Macquarie University's Department of Physics and Astronomy, said in a statement. You can see their final plot in the video below, published in Nature Astronomy.

Prof de Grijs said: 'Somewhat to our surprise, we found in 3D our collection of 1,339 Cepheid stars and the Milky Way's gas disc follow each other closely.

The stars appeared to take on the same shape as the hydrogen gas, warping out to around 50,000 light-years from the Milky Way's centre.

Previously, astronomers saw evidence of hydrogen clouds becoming warped in the Milky Way.

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