[…] The Milky Way is anything but static. It rotates and it wobbles, and new observations from the European Space Agency’s Gaia space telescope now reveal another motion, a giant wave moving outward from the galaxy’s centre.
For roughly a century, astronomers have known that stars orbit the galactic centre, and Gaia has mapped their speeds and paths. Since the 1950s, researchers have recognized that the Milky Way’s disc is warped. In 2020, Gaia showed that this disc also wobbles over time, similar to a spinning top.
It is now clear that a vast ripple influences stellar motions across distances of tens of thousands of light-years from the Sun. Like waves spreading from a stone dropped into a pond, this stellar ripple spans a large stretch of the Milky Way’s outer disc.
The European Space Agency’s (ESA) Gaia space telescope has revealed that our Milky Way galaxy has a giant wave rippling outwards from its center. In the left image, we look at our galaxy from ‘above’. On the right, we see across a vertical slice of the galaxy and look at the wave side-on. In this perspective, the Sun is located between the line of sight and the bulge of the galaxy. This perspective also reveals that the ‘left’ side of the galaxy curves upward and the other side curves downward (this is the warp of the disc). The newly discovered wave is indicated in red and blue: in red areas, the stars lie above, and in blue areas the stars lie below the warped disc of the galaxy. Credit: ESA/Gaia/DPAC, S. Payne-Wardenaar, E. Poggio et al (2025)
The unexpected galactic ripple is illustrated in this figure above. Here, the positions of thousands of bright stars are shown in red and blue, overlaid on Gaia’s maps of the Milky Way.
In the left image, we look at our galaxy from ‘above’. On the right, we see across a vertical slice of the galaxy and look at the wave side-on. This perspective reveals that the ‘left’ side of the galaxy curves upward and the ‘right’ side curves downward (this is the warp of the disc). The newly discovered wave is indicated in red and blue: in red areas, the stars lie above, and in blue areas, the stars lie below the warped disc of the galaxy.
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The Scale of the Wave
From these, we can see that the wave stretches over a huge portion of the galactic disc, affecting stars around at least 30–65 thousand light-years away from the center of the galaxy (for comparison, the Milky Way is around 100 thousand light-years across).
The great wave could also be related to a smaller-scale rippling motion seen 500 light-years from the Sun and extending over 9000 light-years, the so-called Radcliffe Wave.
“However, the Radcliffe Wave is a much smaller filament, and located in a different portion of the galaxy’s disc compared to the wave studied in our work (much closer to the Sun than the great wave). The two waves may or may not be related. That’s why we would like to do more research,” Eloisa adds.
“The upcoming fourth data release from Gaia will include even better positions and motions for Milky Way stars, including variable stars like Cepheids. This will help scientists to make even better maps, and thereby advance our understanding of these characteristic features in our home galaxy,” says Johannes Sahlmann, ESA’s Gaia Project Scientist.
Reference: “The great wave – Evidence of a large-scale vertical corrugation propagating outwards in the Galactic disc” by E. Poggio, S. Khanna, R. Drimmel, E. Zari, E. D’Onghia, M. G. Lattanzi, P. A. Palicio, A. Recio-Blanco and L. Thulasidharan, 14 July 2025, Astronomy & Astrophysics. DOI: 10.1051/0004-6361/202451668
