Westerhout 40

Westerhout 40 is a nearby star-forming complex in Aquila where massive young stars ionize surrounding gas beside dense molecular clouds. Its interacting stellar and gaseous components make it a studied example of triggered star formation.

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H II region: A volume of ionized hydrogen around hot stars, glowing as electrons recombine with protons. The bright nebula in Westerhout 40 is an H II region powered by young massive stars.
Photoionization: The removal of electrons from atoms or molecules after they absorb photons. Ultraviolet photons from Westerhout 40’s young massive stars create its ionized gas.
Sh 2-64: An H II region cataloged in the Sharpless survey of emission nebulae. Sh 2-64 is the nebular designation commonly associated with Westerhout 40’s ionized region.
Karl Gordon Henize: An American astronomer who compiled catalogs of emission-line stars and nebulae. Henize’s catalogs provide an independent historical naming context for emission regions in this part of the sky.
Parallax: The apparent shift in an object's position caused by observing it from different locations. Parallax measurements help constrain Westerhout 40’s distance, which sets its physical scale.
Molecular cloud: A cold, dense interstellar cloud where molecules form and stars can develop. Dense molecular gas borders Westerhout 40’s ionized nebula and supplies material for star formation.
Stellar feedback: The ways stars return energy and momentum to surrounding gas and dust. Radiation and winds from massive stars alter the clouds around Westerhout 40.
W40 IRS 1A: A luminous young stellar object in the Westerhout 40 region, observed at infrared wavelengths. Its infrared emission exemplifies the embedded young sources within Westerhout 40.
Westerhout catalogue: A catalog of radio sources in the Milky Way compiled by Gart Westerhout. Westerhout 40 takes its designation from this catalog of Galactic radio sources.
Molecular spectroscopy: The study of molecules through their characteristic absorption or emission spectra. Molecular-line measurements reveal the clouds’ motions and physical conditions around Westerhout 40.