Like ripples spreading from a rock cast into water, the newly detected galactic wave shifts stars above and below the Milky Way's warped plane. The wave spans 30,000 to 65,000 light-years from the galaxy's centre, a region covering a large fraction of its 100,000-light-year diameter.
"The intriguing part is not only the visual appearance of the wave structure in 3D space, but also its wave-like behaviour when we analyse the motions of the stars within it," said Eloisa Poggio of Italy's National Institute for Astrophysics (INAF), who led the discovery team.
By mapping the positions and vertical movements of young giant stars and Cepheid variables, Gaia revealed a ripple pattern. The stars' motions, indicated by arrows in Gaia's visualisations, are slightly offset from their positions, a hallmark of wave dynamics. "This observed behaviour is consistent with what we would expect from a wave," Poggio explained.
The research team likens the process to a stadium wave frozen in time: some individuals have just stood, others are sitting, and some are rising to join in. Similarly, stars in red regions of Gaia's maps sit above the galactic plane, while blue areas mark stars below it, all shifting with the galactic ripple.
Because Cepheids and young stars move in step with the wave, scientists suspect that gas in the Milky Way's disc is also part of the oscillation. These young stars may have inherited the wave's imprint from the gas clouds that formed them.
The cause of the galactic wave remains unknown. One possible origin is a past collision with a smaller galaxy. Another is a link with the Radcliffe Wave, a closer 9,000-light-year-long filament near the Sun, though the two structures may be unrelated.
"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," said Johannes Sahlmann, ESA's Gaia Project Scientist.
Research Report:Evidence of a large-scale vertical corrugation propagating outwards in the Galactic disc
Related Links
European Space Agency
Stellar Chemistry, The Universe And All Within It
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