Astronomers at Harvard University have discovered a monolithic, wave-shaped gaseous structure — the largest ever seen in our galaxy — made up of interconnected stellar nurseries. Dubbed the “Radcliffe Wave” in honor of the collaboration’s home base, the Radcliffe Institute for Advanced Study, the discovery transforms a 150-year-old vision of nearby stellar nurseries as an expanding ring into one featuring an undulating, star-forming filament that reaches trillions of miles above and below the galactic disk.
The work, published in Nature, was enabled by a new analysis of data from the European Space Agency’s Gaia spacecraft, launched in 2013 with the mission of precisely measuring the position, distance, and motion of the stars. The research team’s innovative approach combined the super-accurate data from Gaia with other measurements to construct a detailed, 3D map of interstellar matter in the Milky Way, and noticed an unexpected pattern in the spiral arm closest to Earth.
The researchers discovered a long, thin structure, about 9,000 light-years long and 400 light-years wide, with a wave-like shape, cresting 500 light-years above and below the mid-plane of our galaxy’s disk. The Wave includes many of the stellar nurseries that were thought to form part of “Gould’s Belt,” a band of star-forming regions believed to be oriented in a ring around the sun.
“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 Robert Wheeler Willson Professor of Applied Astronomy, research associate at the Smithsonian Institution, and co-director of the Science Program at the Radcliffe Institute for Advanced Study. “We were completely shocked when we first realized how long and straight the Radcliffe Wave is, looking down on it from above in 3D — but how sinusoidal it is when viewed from Earth. The Wave’s very existence is forcing us to rethink our understanding of the Milky Way’s 3D structure.”
“Gould and Herschel both observed bright stars forming in an arc projected on the sky, so for a long time, people have been trying to figure out if these molecular clouds actually form a ring in 3D,” said João Alves, a professor of physics and astronomy at the University of Vienna and 2018‒2019 Radcliffe Fellow. “Instead, what we’ve observed is the largest coherent gas structure we know of in the galaxy, organized not in a ring but in a massive, undulating filament. 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.”