The Milky Way flutters

Astronomers discover wave-like up and down movements in our home galaxy

Recording of a speed field by RAVE. The section shows an area perpendicular to the Milky Way. The arrows mark the direction of movement of the stars. The colors signal different speeds. © AIP
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Our home galaxy, the Milky Way, flutters: parts of it also move up and down perpendicular to the galactic disk - much like the fabric of a flag flutters in the wind. This is what astronomers found out when the movements of stars in the neighborhood determined the sun. However, what triggers this fluttering of our galaxy, is still unclear.

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Our home galaxy is in perpetual motion: all the stars and other weird objects in this barred spiral revolve around the galactic center - and with it our star, the sun. She races at just under one million kilometers per hour around the Milky Way Center. The further out a star sits in the galaxy, the faster it moves. But that's not all, as it turns out: The Milky Way also makes small wobbling and fluttering movements up and down - like a flag in the wind.

Glimpse into the galactic neighborhood

The astronomers around Mary Williams of the Leibniz Institute for Astrophysics Potsdam (AIP) discovered fluttering when they examined the velocities of stars around our Sun. As part of the RAdial Velocity Experiment (RAVE), this sky survey covers half a million stars - all stellar neighbors of the Sun. The star field studied for this extends 6, 500 light-years above and below the Sun and covers a quarter of the way to the galactic center.

By determining the distance and speed of the stars, researchers were able to create precise 3D-based motion patterns of stars for the first time. However, these patterns are highly complex. In order to unravel and understand these patterns, astronomers studied the motions of stars above and below the galactic disk. It turned out that the movements and speeds within the Milky Way are more varied than expected. display

Chaotic wave pattern

Thus, the galaxy not only rotates, but parts of it also swing up and down perpendicular to its plane. These vertical movements are based on a wave-like pattern, with stars swirling out to that side. What exactly triggers these movements is so far unclear. However, the researchers suspect that forces acting from different directions are responsible for causing a chaotic wave pattern. These forces may be generated by movements of the spiral arms or by ripples in space-time resulting from the passage of small dwarf galaxies through the Milky Way.

With the new results, it will be possible in the future to create much more accurate 3D models of our galaxy. (Monthly Notices of the Royal Astronomical Society, 2013, in press; arXiv: 1302.2468)

(Leibniz Institute for Astrophysics Potsdam (AIP), 23.10.2013 - NPO)