Giant wave of interconnected stellar nurseries, largest gaseous structure in Milky Way, discovered
A wave-shaped gaseous structure — the largest ever seen in our galaxy and made up of interconnected stellar nurseries — has been discovered by astronomers at Harvard University.
The researchers found 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 previously thought to form part of "Gould's Belt", a band of star-forming regions believed to be oriented around the Sun in a ring.
According to the scientists, the new 3D map shows our galactic neighborhood in a new light, giving researchers a revised view of the Milky Way and opening the door to other major discoveries.
The finding, they say, 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 structure has been dubbed the "Radcliffe wave" in honor of the collaboration's home base, the Radcliffe Institute for Advanced Study, says the study published in Nature.
"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," says Alyssa Goodman, the Robert Wheeler Willson Professor of Applied Astronomy at Harvard University, a research associate at the Smithsonian Institution.
"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,” says Goodman, who is co-director of the science program at the Radcliffe Institute of Advanced Study.
Catherine Zucker, who is an NSF Graduate Fellow and a PhD candidate at Harvard's Graduate School of Arts and Sciences based in Harvard's Department of Astronomy, played a crucial role in compiling the largest-ever catalog of accurate distances to local stellar nurseries, which is the basis for the 3D map used in the study.
"We pulled this team together so we could go beyond processing and tabulating the data to actively visualizing it, not just for ourselves but for everyone. Now, we can literally see the Milky Way with new eyes," says Zucker.
Disentangling structures in the "dusty" galactic neighborhood within which we sit is a long-standing challenge in astronomy.
According to Goodman, scientists have been studying dense clouds of gas and dust between the stars for over a hundred years, zooming in on these regions with ever-higher resolution.
Before Gaia, there were no significant datasets expansive enough to reveal the galaxy's structure on large scales. Since its launch in 2013, the space observatory has enabled measurements of the distances to one billion stars in the Milky Way galaxy.
For the current study, the research team combined data and observations from Gaia with astrostatistics, data visualization, and numerical simulations to construct a detailed, 3D map of interstellar matter in the Milky Way. They noticed an unexpected pattern in the spiral arm closest to the Earth.
“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,” says João Alves, professor of stellar astrophysics at the University of Vienna and Radcliffe Fellow (2018-2019).
"Instead, what we have 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,”
The findings have also been presented at the 235th Meeting of the American Astronomical Society.
"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',” says Alves.