W40 lies in a molecular cloud with an estimated mass of 10⁴ M☉.
The core of the molecular cloud has a shape like a shepherd's crook and is currently producing new stars.
The cluster of OB and pre–main-sequence (PMS) stars lies just eastward of the bend in this filament.
The cloud core was also observed in radio light produced by CO, which allows the mass of the core to be estimated at 200–300 M☉.
A weak, bipolar outflow of gas flows out of the core, likely driven by a young stellar object, with two lobes differing in velocity by 0.5 km/s.

It was in this region where the striking prevalence of filamentary cloud structures seen by ESA's Herschel Space Observatory was first noted.
These filaments of cloud have dense "cores" of gas embedded within them—many of which are likely to gravitationally collapse and form stars.
The Herschel results for this region, and subsequently reported results for other star-forming regions, imply that fragmentation of molecular-cloud filaments are fundamental to the star-formation process.
The Herschel results for W40 and the Aquila Rift, compared to those for molecular clouds in the Polaris region, suggest that star-formation occurs when the linear density (mass per unit length) exceeds a threshold making them susceptible to gravitational instability.
This accounts for the high star-formation rate in W40 and the Aquila Rift, in contrast to the low star-formation rate in the Polaris clouds.
These observational results complement computer simulations of star-formation, which also emphasize the role that molecular-cloud filaments play in the birth of stars.

Observations by the space-based Chandra X-ray Observatory have shown a diffuse X-ray glow from the H II region, which is likely due to the presence of a multi-million Kelvin plasma.
Such hot plasmas can be produced by winds from massive stars, which become shock heated.
W40 lies in a molecular cloud with an estimated mass of 10⁴ M☉. The core of the molecular cloud has a shape like a shepherd's crook and is currently producing new stars. The cluster of OB and pre–main-sequence (PMS) stars lies just eastward of the bend in this filament. The cloud core was also observed in radio light produced by CO, which allows the mass of the core to be estimated at 200–300 M☉. A weak, bipolar outflow of gas flows out of the core, likely driven by a young stellar object, with two lobes differing in velocity by 0.5 km/s.
It was in this region where the striking prevalence of filamentary cloud structures seen by ESA's Herschel Space Observatory was first noted. These filaments of cloud have dense "cores" of gas embedded within them—many of which are likely to gravitationally collapse and form stars. The Herschel results for this region, and subsequently reported results for other star-forming regions, imply that fragmentation of molecular-cloud filaments are fundamental to the star-formation process. The Herschel results for W40 and the Aquila Rift, compared to those for molecular clouds in the Polaris region, suggest that star-formation occurs when the linear density (mass per unit length) exceeds a threshold making them susceptible to gravitational instability. This accounts for the high star-formation rate in W40 and the Aquila Rift, in contrast to the low star-formation rate in the Polaris clouds. These observational results complement computer simulations of star-formation, which also emphasize the role that molecular-cloud filaments play in the birth of stars.
Observations by the space-based Chandra X-ray Observatory have shown a diffuse X-ray glow from the H II region, which is likely due to the presence of a multi-million Kelvin plasma. Such hot plasmas can be produced by winds from massive stars, which become shock heated.
Westerhout 40