This composite image at infrared wavelengths was obtained using the Gemini North laser guide star system in conjunction with the ALTAIR adaptive optics system and the NIRI near-infrared imager. The image shows the Orion "bullets" as blue features and represents the light emitted by hot iron gas. The light from the wakes, shown in orange, is from excited hydrogen gas. Gemini Observatory
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Astronomy.com
March 22, 2007
Excerpted
An image released today by the Gemini Observatory brings into focus a new and remarkably detailed view of supersonic "bullets" of gas and the wakes created as they pierce through clouds of molecular hydrogen in the Orion Nebula. The image was made possible with new laser guide star adaptive optics technology that corrects in real time for image distortions caused by Earth's atmosphere.
The Orion Nebula is a star-forming region located relatively near to us, about 1,500 light-years away. It's a young stellar nursery and shows many unusual features related to the effect of massive stars on the dense birth environment of gas and dust.
The Orion bullets were first seen in a visible-light image in 1983. By 1992, images taken at infrared wavelengths led astronomers to conclude that these clumps of gas were ejected from deep within the nebula following an unknown violent event connected with the recent formation of a cluster of massive stars there. The bullets are speeding outward from the cloud at up to 250 miles (400 kilometers) per second. This is more than a thousand times faster than the speed of sound. The name "bullet" is somewhat misleading since these objects are truly gigantic. The typical size of one of the bullet tips is about ten times the size of Pluto's orbit around the Sun. The wakes shown in the image about are about a fifth of a light- year long.
Clouds of iron atoms at the tip of each bullet glow brightly (blue in the Gemini image) as they are shock-heated by friction to around 9,000º Fahrenheit (5000º Celsius). Molecular hydrogen, which makes up the bulk of both the bullets and the surrounding gas cloud, is destroyed at the tips by the violent collisions between the high-speed bullets and the surrounding cloud. On the trailing edges of the bullets, however, the hydrogen molecules are not destroyed, but instead are heated to about 4000ºF (2000ºC). As the bullets plow through the clouds they leave behind distinctive tubular wakes (colored orange in the Gemini image). These wakes shine like bullet tracers due to the heated molecular hydrogen gas.
