Milky Way galaxy `wobbles`

Washington – An international team of astronomers have discovered that Milky Way galaxy “wobbles.”

The team of astronomers around Mary Williams from the Leibniz Institute for Astrophysics Potsdam (AIP) detected and examined this phenomenon with the RAdial Velocity Experiment (RAVE), a survey of almost half a million stars around the Sun.

In addition to the regular Galactic rotation the scientists found the Milky Way moving perpendicular to the Galactic plane.

The Milky Way 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.

The source of the forces is still not understood however: possible causes include spiral arms stirring things up or ripples caused by the passage of a smaller galaxy through our own.

In this study, RAVE stars were used to examine the kinematics (velocities) of stars in a large, 3D region around the Sun – the region surveys 6500 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 publication has been published in Monthly Notices of the Royal Astronomical Society (MNRAS).