Massive stars inject mechanical and radiative energy into the surrounding environment, which stirs it up, heats the gas, produces cloud and intercloud phases in the interstellar medium, and disrupts molecular clouds (the birth sites of new stars1,2). Stellar winds, supernova explosions and ionization by ultraviolet photons control the lifetimes of molecular clouds3,4,5,6,7. Theoretical studies predict that momentum injection by radiation should dominate that by stellar winds8, but this has been difficult to assess observationally. Velocity-resolved large-scale images in the fine-structure line of ionized carbon ([C ii]) provide an observational diagnostic for the radiative energy input and the dynamics of the interstellar medium around massive stars. Here we report observations of a one-square-degree region (about 7 parsecs in diameter) of Orion molecular core 1—the region nearest to Earth that exhibits massive-star formation—at a resolution of 16 arcseconds (0.03 parsecs) in the [C ii] line at 1.9 terahertz (158 micrometres). The results reveal that the stellar wind originating from the massive star θ1 Orionis C has swept up the surrounding material to create a ‘bubble’ roughly four parsecs in diameter with a 2,600-solar-mass shell, which is expanding at 13 kilometres per second. This finding demonstrates that the mechanical energy from the stellar wind is converted very efficiently into kinetic energy of the shell and causes more disruption of the Orion molecular core 1 than do photo-ionization and evaporation or future supernova explosions.
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The datasets analysed during this study are available through the SOFIA Data Cycle System (https://dcs.arc.nasa.gov/dataRetrieval/SearchScienceArchiveInfoBasic.jsp) and can be retrieved by searching for the PI (Alexander Tielens) and instrument (GREAT).
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We acknowledge the work during the upGREAT square-degree survey of Orion of the USRA and NASA staff of the Armstrong Flight Research Center in Palmdale and of the Ames Research Center in Mountain View, and the Deutsches SOFIA Institut. Research on the interstellar medium at Leiden Observatory is supported through a Spinoza award. We thank the ERC and the Spanish MCIU for funding support under grants ERC-2013-Syg-610256-NANOCOSMOS and AYA2017-85111-P, respectively.
Nature thanks J. Fischer, L. Lopez and the other anonymous reviewer(s) for their contribution to the peer review of this work.
Extended data figures and tables
The 78 tiles indicated were used to construct the final map. The background image is the 70-μm Herschel/PACS dust emission. The yellow contours correspond to an approximated far-ultraviolet radiation field of G0 = 50 (in Habing units). The colour of each tile indicates its corresponding OFF position: blue tiles use the COFF-SE1 position, red tiles use COFF-OFF1 and green tiles use COFF-C. Each square tile has a side length of 435.6 arcsec. The black box at the centre indicates the region mapped by the single-pixel Herschel/HIFI instrument in 9 h55. The total observing time for the SOFIA/upGREAT map was 42 h.
a, Spectrum obtained at the map centre (RA = 5 h 35 min 17 s; dec. = −5° 22′ 16.9″). b, Average spectrum over the entire map.
The locations of the massive stars of the Orion constellation are marked with green stars (shoulders and knees; the belt is indicated by a single star; M42 is at the tip of the sword). The two giant molecular clouds A and B are shown in blue, and the prominent H ii regions are indicated by the green area, which includes M42 and the Trapezium cluster. Barnard’s loop, which is very prominent in Hα, is indicated by the red line. The bubble surrounding λ Ori (grey) is also indicated (red, ionized gas; blue, swept-up molecular shell), as are the boundaries of the superbubble (yellow dashed and dotted lines). Diffuse ionized gas is indicated in grey. The approximate locations of the Orion OB sub-associations—Ia, Ib, Ic and Id—are marked in green. The dotted line labelled b = 0 indicates the Galactic plane.
The approximate boundaries of the Orion OB associations Ib and Ic are indicated by dashed ellipses. The Orion Id association is directly associated with the molecular cloud behind the Orion nebula, M42. The reddish glow is due to the Hα line, which originates from recombinations in the ionized gas of Barnard’s loop. The belt stars and the knees are obvious. The size of the image is approximately 10° on the sky.
Extended Data Fig. 5 Composite infrared and X-ray views of the Orion region of massive star formation.
The [C ii] integrated intensity map is shown by the colour scale. The X-ray emission (from XMM-Newton) is outlined by a green contour. The hot gas probably entirely fills the bubble, but absorption by the Veil extinguishes the left side. The position of θ1 Ori C (RA(J2000) = 5 h 35 min 16.46 s, dec.(J2000) = −5° 23′ 22.8″) is indicated by a blue star.
With increasing vLSR, the shell is displaced outwards, away from the centre of the bubble. This is the kinematic signature of an expanding half-shell. Each colour outlines the emission boundaries of channels 1 km s−1 wide from vLSR = 0 to vLSR = 7 km s−1. The origin (magenta star) corresponds to the position of θ1 Ori C (RA(J2000) = 5 h 35 min 16.46 s, dec.(J2000) = −5° 23′ 22.8″). In the velocity range 4–7 km s−1, [C ii] emission associated with OMC-4 starts to fill in the interior of the bubble. OMC-4 is a star-forming core near the front of the background molecular cloud and is not part of the Veil bubble.
Extended Data Fig. 7 Four exemplary position–velocity diagrams of the [C ii] emission from selected cuts across the Veil.
Each position–velocity diagram exhibits a clear arc structure extending over about 2,500″, which corresponds to the expanding Veil shell (C.P. et al., manuscript in preparation). The left (right) two panels are cuts along the horizontal (vertical) axis.
Left, optical depth map of the dust emission at 160 μm (τ160), which traces the mass of the shell. The two large circles indicate the extent of the shell used to determine the mass of the limb-brightened shell. The small circle (‘OMC1’) circumscribes the Huijgens region associated with the Trapezium stars. We estimated the mass that is enclosed between the two large circles, excluding the Huijgens region. Right, SED of the dust emission observed for different positions in Orion; Fλ is the observed flux. These SEDs are analysed to determine the dust and gas mass. Data and curves represent observed SEDs and model fits for β = 2, respectively. The legend shows the resulting dust temperature Td and τ160. These SED fits were analysed for each spatial point and the resulting τ160 values were used to construct the map shown in the left panel.
These spectra are dominated by the [C ii] line from the main isotope and show the weak hyperfine component of 13C+ near vLSR = 20 km s−1. This line is used to estimate the optical depth of the main isotope line and thus the mass of the emitting gas. The red spectrum corresponds to the area between the two large circles in Extended Data Fig. 8, but excluding Huijgens region in the small circle. The blue spectrum is an average over the bright parts in the eastern shell, in the declination range −5° 35′ to −5° 45′. The inset shows a close-up of the (faint) [13C ii] line in the average shell spectrum.