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How do radio waves reveal the shape of the Orion Nebula through dust?

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H II region Centre of the Orion Nebula (M42). Astronomers have identified some 700 young stars in this 2.5-light-year-wide area. They have also detected over 150 protoplanetary disks, or proplyds, which are believed to be embryonic solar systems that will eventually form planets. These stars and proplyds generate most of the nebula's light. This picture is a mosaic combining 45 images taken by the Hubble Space Telescope.

At visible wavelengths, the Orion Nebula appears to have an irregular shape, but this is largely a visual illusion caused by dark foreground dust that obscures approximately half of the ionized gas.1

Because radio waves are capable of penetrating this thick, obscuring dust unhindered, astronomers can use them to observe the underlying structure of the nebula. When viewed through radio emissions, the ionized gas is revealed to be quite circular in shape and surprisingly symmetrical as seen in projection on the sky.12