Our Sun lies within 300 parsecs (around 1,000 light-years) of the 2,700-parsec- (around 9,000-light-year-) long sinusoidal chain of dense gas clouds known as the Radcliffe Wave. The structure’s wave-like shape was discovered using 3D dust mapping, but initial kinematic searches for oscillatory motion were inconclusive. According to new research, the Radcliffe Wave is oscillating through the plane of our Milky Way Galaxy while also drifting radially away from the Galactic center.
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The Radcliffe Wave next to our Sun (yellow dot), inside a cartoon model of the Milky Way. Blue dots are clusters of baby stars. The white line is a theoretical model by Konietzka et al. that explains the current shape and motion of the wave. The magenta and green lines show how the wave will move in the future. Image credit: Ralf Konietzka / Alyssa Goodman / WorldWide Telescope.
“By using the motion of baby stars born in the gaseous clouds along the Radcliffe Wave, we can trace the motion of their natal gas to show that the Radcliffe Wave is actually waving,” said Ralf Konietzka, a Ph.D. student at the Harvard & Smithsonian’s Center for Astrophysics.
In 2018, astronomers mapped out the 3D positions of the stellar nurseries in the Sun’s galactic neighborhood.
By combining brand-new data from ESA’s Gaia mission with the data-intensive ‘3D dust mapping’ technique, they noticed a pattern emerging, leading to the discovery of the Radcliffe Wave in 2020.
“It’s the largest coherent structure that we know of, and it’s really, really close to us,” said Dr. Catherine Zucker, an astronomer at the Harvard & Smithsonian’s Center for Astrophysics.
“It’s been there the whole time. We just didn’t know about it, because we couldn’t build these high-resolution models of the distribution of gaseous clouds near the Sun, in 3D.”
The 3D dust map clearly showed that the Radcliffe Wave existed, but no measurements available then were good enough to see if the wave was moving.
But in 2022, using a newer release of Gaia data, the astronomers assigned 3D motions to the young star clusters in the Radcliffe Wave.
With the clusters’ positions and motions in hand, they were able to determine that the entire Radcliffe Wave is indeed waving, moving like what physicists call a ‘traveling wave.’
“A traveling wave is the same phenomenon we see in a sports stadium when people stand up and sit down in sequence to do the wave,” Konietzka said.
“Likewise, the star clusters along the Radcliffe Wave move up and down, creating a pattern that travels through our galactic backyard.”
“Similar to how fans in a stadium are being pulled back to their seats by the Earth’s gravity, the Radcliffe Wave oscillates due to the gravity of the Milky Way.”
No one yet knows what caused the Radcliffe Wave or why it moves the way it does.
“Now we can go and test all these different theories for why the wave formed in the first place,” Dr. Zucker said.
“Those theories range from explosions of massive stars, called supernovae, to out-of-galaxy disturbances, like a dwarf satellite galaxy colliding with our Milky Way,” Konietzka added.
“It turns out that no significant dark matter is needed to explain the motion we observe.”
“The gravity of ordinary matter alone is enough to drive the waving of the wave.”
In addition, the discovery of the oscillation raises new questions about the preponderance of these waves both across the Milky Way and other galaxies.
Since the Radcliffe Wave appears to form the backbone of the nearest spiral arm in the Milky Way, the waving of the wave could imply that spiral arms of galaxies oscillate in general, making galaxies even more dynamic than previously thought.
“The question is, what caused the displacement giving rise to the waving we see?” said Professor Alyssa Goodman, an astronomer at the Harvard & Smithsonian’s Center for Astrophysics.
“And does it happen all over the galaxy? In all galaxies? Does it happen occasionally? Does it happen all the time?”
The results appear in the journal Nature.
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R. Konietzka et al. The Radcliffe Wave is Oscillating. Nature, published online February 20, 2024; doi: 10.1038/s41586-024-07127-3
