It’s Not Just You – The Galaxy IS Warped, After All!

The Milky Way is warped at its edges according to the first detailed 3-D map made of our home galaxy. The idea that we live in a thin, flat spiral galaxy now needs to be supplanted by a more interesting, and complex, idea of a disk twisted at its ends.

Macquarie University researchers, together with investigators from the Chinese Academy of Sciences, used the positions of 1,339 stars to create the new map. This model revealed the galaxy is mostly flat near the center, becoming more warped toward the edges.

“We usually think of spiral galaxies as being quite flat, like Andromeda which you can easily see through a telescope,” said Professor Richard de Grijs, astronomer from Macquarie University.

This is a slightly-exaggerated concept of how the Milky Way actually looks, if seen nearly-edge-on. Image credit: Chao Liu (National Astronomical Observatories, Chinese Academy of Sciences)

For 50 years, astronomers have seen evidence that clouds of hydrogen in the Milky Way Galaxy were located in a warped pattern. For this study, astronomers examined data showing the locations of classical Cepheid stars, each up to 20 times more massive, and 100,000 times brighter, than our Sun. These hot, short-lived, stellar bodies are typically used by astronomers measuring distances to groups of stars. The information utilized for this new map was collected by the Wide-field Infrared Survey Explorer (WISE), a NASA telescope launched in December 2009.

“It is notoriously difficult 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 Xiaodian Chen, a researcher at the Chinese Academy of Sciences in Beijing.

Galaxies come in three main shapes, spiral (like our own Milky Way), elliptical, and irregular. Spiral galaxies are marked by a central core, known as a nuclear bulge. This feature is surrounded by twisted arms, each containing several tens of billions of stars. Our Sun is located two-thirds of the way to the edge of the Milky Way.

M74 Seen with the Hubble Space Telescope (HST)
M74, viewed by the Hubble Space Telescope, is a spiral galaxy, somewhat like the Milky Way. Image credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

Both the core and the inner arms of spiral galaxies are surrounded by a loose halo of stars, containing groups of old stars, called globular clusters. Nearly every galaxy, of all types, is now thought to house a supermassive black hole at its center.

Young stars seen in the warped disk of the galaxy suggest the warped “s-shaped” pattern is likely caused by torque created by stars in the inner-most part of our galaxy, orbiting the galactic core. Astronomers have seen similar twisting in other galaxies, suggesting this warped shape is rare, but not unheard of, among large families of stars.

Analysis of the findings was published in the journal Nature Astronomy.


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