The Radcliffe Wave
A graphic of the extended molecular cloud structure discovered in the solar neighborhood, as viewed from a position in the Milky Way looking at it sideways. This long sinusoidal feature stretches over about nine thousand light-years, and replaces an older view of a Gould Belt ring of star formation. The red points are the objects that were measured and fitted to a new three-dimensional algorithm.
The Gould Belt is an expanding ring of young stars, gas and dust situated about a thousand light-years from the Sun - which is to say, in our solar neighborhood. It stretches over a few thousand light-years and is thought to subsume many famous nearby nebulae like the one in Orion. The physical relationships between its many gas clouds, if any, have been unknown because the uncertainties in their distances are comparable to or even larger than their dimensions.
CfA astronomers Catherine Zucker, Alyssa Goodman, Josh Speagle, and Doug Finkbeiner and their colleagues used new astrometric surveys like the Gaia mission, coupled with detailed analyses of stellar brightenesses, colors, and distances to construct three-dimensional maps of the Milky Way around the Gold Belt to higher accuracies than ever before. The new distance information reveals for the first time the three-dimensional structure of the clouds in the solar neighborhood, including the presumptive Gould Belt clouds and others like the North American Nebula that had not been previously associated with the Gould Belt. They discovered that the clouds are not quasi-randomly distributed in a ring, as had been thought, but rather form a dramatic, elongated structure stretching about nine thousand light-years in length. The formation includes the majority of nearby star-forming regions, has an aspect ratio of about twenty-to-one, and contains about three million solar masses of gas. Most remarkably, this structure appears to be undulating, with a three-dimensional shape well described by a damped sinusoidal wave on the plane of the Milky Way with an average period of about seven thousand light-years and a maximum amplitude of about five hundred light-years.
The astronomers have named the structure the Radcliffe Wave in honor of both the early-20th-century female astronomers from Radcliffe College and the interdisciplinary spirit of the current Radcliffe Institute, which contributed to the discovery. The origin of the Radcliffe Wave is unclear but the scientists speculate that it could be the outcome of a large-scale galactic process, perhaps a shock front in the galaxy's nearby spiral arm. Why it should be such a well-defined wave, however, is even harder to explain; possibly it implies some sort of collision. The Radcliffe Wave provides a new framework for understanding molecular cloud formation and evolution. The team concludes by calling for a revision in the architecture of the gas in the solar neighborhood and a re-interpretation of other local structural phenomena.
"A Galactic-Scale Gas Wave in the Solar Neighbourhood," João Alves, Catherine Zucker, Alyssa A. Goodman, Joshua S. Speagle, Stefan Meingast, Thomas Robitaille, Douglas P. Finkbeiner, Edward F. Schlafly & Gregory M. Green, Nature, 578, 237, 2020.