Astronomers have discovered the largest gas structure in the Milky Way, which stretches for 9,000 light-years and measures 400 light-years across. The structure connects stellar nurseries throughout its length and goes up and down the Milky Way’s disk like a wave, reaching 500 light-years both above and below it.
As reported in Nature, the discovery finally clarifies a 150-year-old idea. Some of the stellar nurseries in the wave appear as an arc across the sky, the so-called Gould’s Belt, and astronomers had been wondering if it was part of a 3D ring. The answer was even more surprising and also very close to home.
“The Sun lies only 500 light-years from the Wave at its closest point. It’s been right in front of our eyes all the time, but we couldn’t see it until now,” lead author Professor João Alves, from the University of Vienna, said in a statement.
“We don’t know what causes this shape, but it could be like a ripple in a pond, as if something extraordinarily massive landed in our galaxy. What we do know is that our Sun interacts with this structure. It passed by a festival of supernovae as it crossed Orion 13 million years ago, and in another 13 million years it will cross the structure again, sort of like we are ‘surfing the wave.’”
The discovery was possible thanks to incredible observations from the European Space Agency’s Gaia observatory, which is measuring the precise distances and velocities of over a billion stars in the Milky Way. To truly unlock the potential of the data, the team had to use new approaches to refine the distances between these star-forming regions and us.
“We suspected there might be larger structures that we just couldn’t put in context," explained graduate researcher Catherine Zucker, who with fellow researcher Joshua Speagle augmented these statistical techniques. "So, to create an accurate map of our solar neighborhood, we combined observations from space telescopes like Gaia with astrostatistics, data visualization, and numerical simulations.”
In the pursuit of understanding Gould’s Belt, now nicknamed the Radcliffe Wave, the team had to compile the largest-ever catalog of accurate distances to local stellar nurseries. Every star was formed in regions very much like these. This novel understanding will have profound consequences although finding something as incredible as the Wave might take some time.
“No astronomer expected that we live next to a giant, wave-like collection of gas – or that it forms the local arm of the Milky Way,” said Alyssa Goodman, the professor of applied astronomy at Harvard, research associate at the Smithsonian Institution, and co-director of the Science Program at the Radcliffe Institute for Advanced Study. “The Wave’s very existence is forcing us to rethink our understanding of the Milky Way’s 3D structure.”