Radcliffe wave

The Radcliffe wave is a neighbouring 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] This structure runs with the trajectory of the Milky Way arms.^[3][4]

It lies at its closest (the Taurus Molecular Cloud) at around 400 light-years and at its farthest about 5,000 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.^[5][4] Its discovery was announced in January 2020, and its proximity surprised astronomers.^[1][6]

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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][7] 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 which contained the 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]

The wave was discovered by an international team of astronomers including Catherine Zucker and João Alves.^[8][4] It was announced by co-author Alyssa A. Goodman at the 235th meeting of the American Astronomical Society, held at Honolulu^[9] and published in the journal Nature on 7 January 2020.^[10] The discovery was made using data collected by the European Space Agency's Gaia space observatory.^[11]

The wave was invisible in 2D, requiring new 3D techniques of mapping interstellar matter to reveal its pattern using Glue (software).^[2][11][9] The proximity of the wave surprised astronomers.^[1][6] It is named after the Radcliffe Institute for Advanced Study in Cambridge, Massachusetts, the place of study of the team.^[11]

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

• Orion molecular cloud complex
• Perseus molecular cloud
• Taurus molecular cloud
• Cepheus OB2

The cloud not within its scope is the Rho Ophiuchi Cloud complex, part of a linear structure parallel 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 8,800 light-years (2,700 parsecs) and an amplitude of 520 light-years (160 parsecs). 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]

A 2024 paper announced the discovery that the Radcliffe wave is oscillating in the form of a traveling wave.^[12]

• Antlia 2, another giant ripple across the Milky Way's disc found in data from the Gaia space telescope
• List of nearby stellar associations and moving groups
• Great Rift (astronomy)
• Serpens-Aquila Rift

• Alves, João; Zucker, Catherine; Goodman, Alyssa A.; Speagle, Joshua S.; Meingast, Stefan; Robitaille, Thomas; Finkbeiner, Douglas P.; Schlafly, Edward F.; Green, Gregory M. (2020). "A Galactic-scale gas wave in the solar neighborhood". Nature. 578 (7794): 237–239. arXiv:2001.08748. Bibcode:2020Natur.578..237A. doi:10.1038/s41586-019-1874-z. PMID 31910431.

• Interactive map of the Radcliffe wave on the sky
• The Radcliffe Wave informational site created by Harvard University