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It spans somewhere between 30,000 and 65,000 light-years from the center.
A fresh analysis of data from the European Space Agency’s Gaia mission has offered an unexpected look at how our galaxy behaves.
Astronomers already knew the Milky Way rotates and tilts, but the latest findings point to a sweeping, ripple-like motion travelling across its disc.
For decades, scientists have charted the orbits of stars around the galactic centre. Gaia’s precision allowed researchers to refine this picture and, in 2020, confirm that the disc itself slowly oscillates.
Now the same mission has uncovered a new pattern: a large-scale wave that moves outward across tens of thousands of light-years.
A shifting disc
According to ESA’s reporting on the study, the wave behaves like ripples expanding from a stone dropped into water, though in this case the “ripples” involve vast populations of stars far beyond the Sun’s neighbourhood.
Visualisations created from Gaia’s measurements show red and blue regions marking where stars sit above or below the warped disc.
Researchers combined top-down and side-on reconstructions to map how the disc bends.
The left half of the Milky Way arcs upward while the opposite side curves down, and the newly identified wave sits along this distorted plane.
The structure spans roughly 30,000 to 65,000 light-years from the centre, a significant portion of the galaxy’s 100,000-light-year width.
Motion in the map
Eloisa Poggio of Italy’s National Institute for Astrophysics, who led the research team, told ESA that Gaia’s ability to record full 3D positions and motions was decisive.
“What makes this even more compelling is our ability, thanks to Gaia, to also measure the motions of stars within the galactic disc,” she said in an article from ESA.
The group compared the stars’ locations with their vertical movements. White arrows marking those motions appear slightly offset from the red and blue regions, a pattern Poggio described as consistent with wave behaviour.
She likened the effect to a stadium crowd performing a coordinated wave: some people rising, others settling, and others poised to move.
Searching for a cause
To track the disturbance, the team focused on young giant stars and Cepheid variables, whose regular brightness changes help Gaia detect them across large distances.
Their motion suggests that gas in the disc could also be travelling with the wave, preserving a “memory” of the movement as new stars form.
The origin of the oscillation is still being explored. ESA notes that a past brush with a smaller galaxy is one possibility, though evidence remains incomplete.
Researchers are also weighing whether the structure could be linked to the much smaller Radcliffe Wave closer to the Sun, but the connection is uncertain.
What comes next
Johannes Sahlmann, Gaia Project Scientist at ESA, said the mission’s upcoming fourth data release will sharpen star positions and motions further, potentially revealing how these features developed and whether more waves are hidden in the Milky Way’s disc.
You can read the paper on the discovery in Astronomy & Astrophysics right here (opens new tab).
Sources: ESA, mission statements and research summaries, Science Daily
