The Radcliffe wave is the nearest coherent gaseous structure in the Milky Way, dotted with a related high concentration of interconnected stellar nurseries. It stretches about 8,800 light years.[1][2] It runs with the trajectory of the Milky Way arms, and lies at its closest (the Taurus Molecular Cloud) at around 400 light-years and at its farthest about 5000 light-years (the Cygnus X star complex) from the Sun, always within the Local Arm (Orion Arm) itself, spanning about 40% of its length and on average 20% of its width.[3][4] Its discovery was announced in January 2020 and its proximity surprised astronomers.[1][5]

## Formation

The nearby circa one-sixth outer sector of the galaxy, thus clearly showing the Local Arm (Orion Arm) and neighboring arms - as well as the Great Orion Nebula (as a very luminous feature of the less bright Orion Molecular Cloud Complex) and broad-clouds North America Nebula (and Pelican Nebula) which is an intrinsic part of the Radcliffe wave, (clickable map)

Scientists do not know how the undulation of dust and gas formed; it has been suggested that it could be a result of a much smaller galaxy colliding with the Milky Way, leaving behind "ripples", or could be related to dark matter.[1][6] Inside the dense clouds, gas can be so compressed that new stars are born;[2] it has been suggested that this may be where the Sun originated.[1]

Many of the star-forming regions found in the Radcliffe wave were thought to be part of a similar-sized but somewhat helio-centric ring in which sat our solar system, "the Gould Belt". It is now understood the nearest, discrete, relative concentration of sparse interstellar matter instead forms a massive wave.[1][2]

## Discovery

The wave was discovered by an international team of astronomers including Catherine Zucker and João Alves.[7][4] It was announced by co-author Alyssa A. Goodman at the 235th meeting of the American Astronomical Society, held at Honolulu[8] and published in the journal Nature on 7 January 2020.[9] The discovery was made using data collected by the European Space Agency's Gaia space observatory.[10] The wave was invisible in 2D, requiring new 3D techniques of mapping interstellar matter to reveal its pattern.[2][10][8] The proximity of the wave surprised astronomers.[1][5] It is named after the Radcliffe Institute for Advanced Study in Cambridge, Massachusetts, the place of study of the team.[10]

## Overview

The Radcliffe wave contains four of the five Gould Belt clouds, the:

The cloud not within its scope is the Rho Ophiuchi Cloud complex, part of a parallel, linear structure to the Radcliffe wave.

Other structures in the wave, further from the local star system, are Canis Major OB1, the North America Nebula and Cygnus X.[4]

The mass of this structure is on the scale of ${\displaystyle \geq 3\times 10^{6}}$ M. It has a length of 8.8 kilolight-years (2.7 kpc) and an amplitude of 520 light-years (160 parsec). The Radcliffe wave occupies about 20% of the width and 40% of the length of the local arm (Orion Arm). The latter is more dispersed as to its interstellar medium than the wave and has further, large, star-forming regions such as Monoceros OB1, California Nebula, Cepheus Far, and Rho Ophiuchi.[4]