New Gaia analysis finds a large-scale vertical wave rippling across the Milky Way's outer disk. Two independent samples — ~17,000 young giants (to ~23,000 ly) and ~3,400 Cepheids (to ~49,000 ly) — show the same alternating vertical-velocity pattern. The wave's amplitude increases with distance from the galactic center. A past encounter with the Sagittarius dwarf galaxy is a prime candidate trigger, though links to the Radcliffe Wave remain uncertain. The team will re-examine the signal with Gaia DR4 (expected Dec 2026).
A Giant Vertical Wave Is Rippling Through the Milky Way, Gaia Data Shows
New Gaia analysis finds a large-scale vertical wave rippling across the Milky Way's outer disk. Two independent samples — ~17,000 young giants (to ~23,000 ly) and ~3,400 Cepheids (to ~49,000 ly) — show the same alternating vertical-velocity pattern. The wave's amplitude increases with distance from the galactic center. A past encounter with the Sagittarius dwarf galaxy is a prime candidate trigger, though links to the Radcliffe Wave remain uncertain. The team will re-examine the signal with Gaia DR4 (expected Dec 2026).
14:05, 05.11.2025Science
A Giant Vertical Wave Is Rippling Through the Milky Way
New analysis of stellar motions measured by the Gaia space observatory reveals a coherent, large-scale vertical ripple propagating across the outer disk of the Milky Way. By tracking the up-and-down velocities of tens of thousands of stars, astronomers have identified an alternating pattern of peaks and troughs — a corrugation that grows stronger at greater distances from the galactic center.
What the researchers used
The study, led by Eloisa Poggio at the Italian National Institute for Astrophysics, combined Gaia DR3 astrometry with complementary surveys and pulsating-star catalogs. The team analyzed two independent stellar samples: about 17,000 young giant stars reaching to ~23,000 light-years from the Sun, and roughly 3,400 classical Cepheid variables extending to ~49,000 light-years. Given the Milky Way's stellar disk spans ~100,000 light-years, these samples provide substantial radial coverage of the outer disk.
What they found
Both samples display the same coherent vertical velocity pattern — alternating peaks and troughs reminiscent of ripples on a pond. The amplitude of these oscillations increases with radius, so stars in the outer disk move higher above and deeper below the galactic plane than stars closer in. The authors interpret this as evidence for a vertical wave propagating away from the galactic center.
"This wave, detected in young stellar populations, could primarily be part of the gaseous component of the galactic disk, revealed by the kinematics of the young stars which have inherited the bulk motions of the gas from which they were born," the team writes.
Possible causes
The trigger for the ripple is not yet certain. A leading candidate is an interaction with another galaxy — most plausibly the Sagittarius dwarf galaxy, which is currently interacting with the Milky Way and has passed through the disk in the past. Another possibility is a connection with the Radcliffe Wave, a 9,000-light-year filament along one spiral arm; however, the Radcliffe Wave is much smaller and located in a different portion of the disk, so a relation is unclear.
Why this matters
These results reinforce a changing view of the Milky Way as a dynamically active system shaped by past and ongoing interactions rather than a static, placid disk. Vertical waves reveal how the disk responds to perturbations and can help reconstruct the galaxy's recent encounter history.
The study has been published in Astronomy & Astrophysics. The team expects to revisit the phenomenon with the next Gaia release, DR4, currently scheduled for December 2026, when a larger and more precise dataset should help pinpoint the wave's origin and dynamics.