The Radcliffe wave is a coherent, wave-shaped gaseous structure in the Milky Way, made up of interconnected stellar nurseries, stretching over 9000 light years across.[1][2] It is the largest gaseous structure ever seen in the disk of the Milky Way, and lies around 500 light-years from the Sun.[3] Its discovery was announced in January 2020 and its close proximity to the Sun surprised astronomers.[1][4]

## Formation

Scientists do not know how the undulating wave 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][5] 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 previously thought to be part of a huge ring around the solar system known as the Gould Belt, but it is now understood that there is no ring, but a massive wave instead.[1][2] It forms the local arm of the Milky Way.[6]

## Discovery

The Radcliffe wave was discovered by an international team of astronomers including Catherine Zucker and João Alves.[7] It was announced by co-author Alyssa A. Goodman at the 235th meeting of the American Astronomical Society in 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.[6] The wave was invisible in 2D, requiring new 3D techniques of mapping interstellar matter to reveal the wave pattern.[2][6][8] The close proximity of the Radcliffe wave to the Sun surprised astronomers.[1][4] It is named after the Radcliffe Institute for Advanced Study in Cambridge, Massachusetts, where the astronomers are based.[6]

## Overview

The Radcliffe wave contains 4/5 of the Gould Belt clouds: the Orion Molecular Cloud Complex, Perseus Molecular Cloud, the Taurus Molecular cloud and Cepheus OB2. There is one cloud that is not part of the Radcliffe wave: The Rho Ophiuchi Cloud complex is part of a second parallel linear structure to the Radcliffe wave. Other structures that are contained in the Radcliffe wave, but that are further away from Earth are Canis Major OB1, the North America Nebula and Cygnus X.[10]

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 is about 20% of the width and 40% of the length of the local arm. The local arm is more dispersed than the Radcliffe wave and contains several additional large star-forming regions (e.g. Monoceros OB1, California Nebula, Cepheus Far, Rho Ophiuchi) that are not part of the Radcliffe wave.[10]