A giant 'wave' is rippling through the Milky Way, pushing thousands of stars across the galaxy, and scientists don't know what triggered it.

© ESA/Gaia/DPAC, S. Payne-Wardenaar, E. Poggio et al (2025)An edge-on visual of the Milky Way, based on data from the European Space Agency's Gaia star-mapping mission. An apparent "wave" of star movements is visible, shown by vertical arrows.
A huge "wave" is rippling through our galaxy, pushing billions of stars in its wake, a new study reveals.
The
Milky Way's galactic wave was spotted in mapping data from the
European Space Agency's (ESA) Gaia space telescope, which charted the positions and movement patterns of millions of stars with high accuracy before
retiring earlier this year.
Like ripples in a pond, the wave has a very large influence: It affects stars between 30,000 and 65,000 light-years away from the galaxy's center, ESA officials said in a
statement. That's a large percentage of the
Milky Way, which is roughly 100,000 light-years across.
Astronomers still don't know what started the motion. It could have been a
past collision with a smaller, dwarf galaxy that caused the large shake, ESA officials said, but more investigation is required to answer that question.
The results were published July 14 in the journal
Astronomy & Astrophysics.