The Milky Way is being warped and twisted, study says

Artist impression of a warped Milky Way. Credit CHEN Xiaodian

Artist impression of a warped Milky Way. Credit CHEN Xiaodian

It turns out that the further the stars are from the center of the galaxy, the weaker their gravitational pull is. Artist's impression above of the warped and twisted Milky Way disk.

The sun and its planets, including the Earth, occupy an insignificant spot in one of the minor spiral arms.

The Milky Way is warped and twisted rather than flat like a celestial pancake, according to the most accurate 3D map of the galaxy yet.

"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. Normally, it's hard to tell if a star is truly bright or simply close, truly dim or simply very far away.

The paper, published in Nature Astronomy on February 4, details work by Australian and Chinese astronomers to examine the classical "Cepheids" - a collection of huge, young stars in the Milky Way that can be up to 100,000 times brighter than the sun.

To create their map, the team employed the help of 1,339 large pulsating stars known as Classical Cepheids, which are 20 times as massive as our Sun and up to 100,000 times as bright. 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.

A 3D distribution of the classical Cepheids in the Milky Way's warped disk. Credit CHEN Xiaodian
A 3D distribution of the classical Cepheids in the Milky Way’s warped disk. Credit CHEN Xiaodian

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. A dozen other galaxies had previously been shown to display similar warping, the researchers reported today (Feb. 4) in the journal Nature Astronomy.

3D distribution of the classical Cepheid variable stars in the Milky Way's warped disc (red and blue points) centred on the location of the Sun (shown as a large orange symbol).

But, for the past 50 years there have been indications that the hydrogen clouds in the Milky Way are warped. Since hydrogen atoms in the far outer disk are no longer confined to a thin plane, they get warped. "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.

"This research provides a crucial updated map for studies of our galaxy's stellar motions and the origins of the Milky Way's disk", says Licai Deng, senior researcher at the Chinese Academy of Sciences and co-author on the paper. You can see their final plot in the video below, published in Nature Astronomy. 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.

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". Looking at 1,339 Cepheid stars from that catalog, the scientists discovered that their positions reveal a warping at the outer edges of the galaxy.

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