ESA’s Gaia data release 3 shows us the speed at which more than 30 million Milky Way stars move towards or away from us. This is called ‘radial velocity’ and it is providing the third velocity dimension in the Gaia map of our galaxy. We can now see how the stars move over a large portion of the Milky Way’s disc.

Thanks to Gaia, we can clearly see that the stars on average do not rotate with circular motions around the centre of the galaxy. This is because our Milky Way is not symmetric around its axis. It is a ‘barred’ spiral galaxy, and the motions reveal the orientation of the central bar.

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Acknowledgements

Author:              Alex Lobel - Royal Observatory of Belgium

Simulations:       Gaia Sky, GNU Image Manipulation Program (GIMP free open-source)

Illustrations:       Drawing of the Milky Way by R. Hurt and R. Benjamin, 2009

                          Gaia Data Release 3: Mapping the asymmetric disc of the Milky Way - Gaia Collaboration, R. Drimmel, et al. 2022”