Published: Tue, February 05, 2019
Science | By

The Milky Way in a twist

The Milky Way in a twist

The first accurate 3D map of our galaxy reveals its true shape: warped and twisted.

Until now, the galaxy was generally thought to be a flat spiral consisting of an estimated 250 billion stars. "This offers new insights into the formation of our home galaxy", says Prof. Data on these classical Cepheid stars were provided by the Wide-field Infrared Survey Explorer (WISE).

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.

A new study by the National Astronomical Observatories of Chinese Academy of Sciences (NAOC) might explain the Milky Way's spiral appearance - it's warped.

The same twisted spiral patterns have been seen before in more than a dozen other galaxies. That means that if you know the pulsation period, you can infer the star's actual luminosity, then compare that with the luminosity observed from Earth in order to determine the distance.

But the research solidifies something that you might not know about our galaxy-if you picture it as a handsome, flat spiral akin to images of Andromeda, it's time to repaint that picture as a floppy, curved disk of stars and gas.

From a great distance, our galaxy would look like a thin disk of stars that orbit once every few hundred million years around its central region, where hundreds of billions of stars provide the gravitational "glue" to hold it all together.

But the pull of gravity becomes weaker far away from the Milky Way's inner regions.

"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 resulting resource enabled the team to predict that the hydrogen gas in the outer reaches of the disk was not confined to a thin plane but would actually appear like a warped S-shape if observed from a distance.

Richard de Grijs, an astronomer at Macquarie University in Sydney, said the stars showed how the Milky Way has become progressively twisted in its outer regions, an effect most likely caused by the galaxy's massive inner disc unleashing powerful rotational forces.

The research team showed, with the help of the Cepheids, how the Milky Way isn't a flat cosmic disk shaped like a lipless frisbee or a pancake, but instead it's markedly warped into an S-like shape.

"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. And with the amount of stars in the Milky Way increasing thanks to observations by spacecraft such as the European Space Agency's Gaia, there's always room to improve the model even more.

The full findings of the study were published in the journal Nature Astronomy.

Scientists at the Instituto de Astrofísica de Canarias (IAC) in Spain believe that it might have formed about 300 million years after the "Big Bang". Now, researchers have created a map of stars called Cepheid variables in order to create a 3D map of our galaxy and understand the warping better than ever.

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