Milky Way galaxy 'wobbles'

Astronomers have discovered that besides being permanently in motion, our Milky Way galaxy also makes small wobbling or squishing movements.
Being a barred spiral galaxy, Milky Way rotates around the Galactic centre. In addition to the regular Galactic rotation, scientists found the Milky Way moving perpendicular to the Galactic plane.
The galaxy makes small wobbling or squishing movements. It acts like a Galactic mosh pit or a huge flag fluttering in the wind, north to south, from the Galactic plane with forces coming from multiple directions, creating a chaotic wave pattern, researchers said.
However, the source of the forces is still not understood. Possible causes include spiral arms stirring things up or ripples caused by the passage of a smaller galaxy through our own.

An international team of astronomers, including Mary Williams from the Leibniz Institute for Astrophysics Potsdam (AIP) in Germany, detected and examined this phenomenon with the RAdial Velocity Experiment (RAVE), a survey of almost half a million stars around the Sun.
In the study, RAVE stars were used to examine the kinematics (velocities) of stars in a large, 3D region around the Sun - the region surveys 6,500 light years above and below the Sun's position as well as inwards and outwards from the Galactic centre, reaching a quarter of the way to the centre.

Using a special class of stars, red clump stars, which all have about the same brightness, mean distances to the stars could be determined.

This was important as then the velocities measured with RAVE, combined with other survey data, could be used to determine the full 3D velocities (up-down, in-out and rotational).
The RAVE red clump giants gave an unprecedented number of stars with which it is possible to study 3D velocities in a large region around the Sun.
The 3D movement patterns obtained showed highly complex structures. Researchers then concentrated on differences between the north and south of the Galactic plane.
From these velocities it was seen that our Galaxy has a lot more going on than previously thought. The velocities going upwards and downwards show that there is a wave-like behaviour, with stars sloshing in and out.

The study was published in Monthly Notices of the Royal Astronomical Society (MNRAS).