A 9,000-light-year-long ribbon of matter undulates through our sun’s interstellar neighborhood, made of hundreds of different clouds of dust and gas—the largest such structure of interacting nebulae yet described. Its discovery, announced today by a team of Harvard astronomers in the journal Nature, re-draws the map of our corner of the Milky Way and raises new questions about how stars and nebulae form and move through our galaxy, and those beyond.
The structure, dubbed the “Radcliffe Wave,” after Harvard’s Radcliffe Institute for Advanced Study, crests some 500 light years “above” the central disk of our spiral galaxy, before plunging just as far below. It holds about three million times the mass of the sun, mostly in clouds of dust and gas so diffuse they would register as a vacuum by any earthly standard. Never before have scientists seen interstellar clouds organized in a wave-like pattern like this one, but the team thinks that this wave is the backbone of the Orion Arm, the spiral arm of the Milky Way to which our sun belongs.
“We don’t know what causes this shape,” said João Alves, lead author of the Nature paper and a 2018-19 Radcliffe Fellow, in a statement. The professor of stellar astrophysics at the University of Vienna added, “[I]t could be like a ripple in a pond, as if something extraordinarily massive landed in our galaxy.”
“We have no precedent for this sort of structure in the galaxy,” said coauthor Catherine Zucker, a fifth-year doctoral student in astronomy at Harvard, in a separate interview, nor have wave-like structures such as this “been seen yet in simulations of galaxies like our Milky Way.”
The Harvard team found the wave after building the most accurate map to date of the interstellar clouds within about 7,000 light years of the sun. The map made it possible for the first time to visualize more than two billion cubic light years in three dimensions—and brought the massive wave into clear view. “I’m sure you’re wondering why, if this thing is right up in our face, we didn’t find it sooner,” coauthor Alyssa Goodman, Wilson professor of applied astronomy, said in a press conference. “It’s not apparent in 2-D” images of the sky. (Readers can explore an interactive view of the wave for themselves through 3-D visualizations that the authors have posted online.)