HI and HII Regions (2) ...
The Trifid Nebula
The above Limber Observatory image shows an HII region called
the Trifid Nebula imaged in normal light (left) and imaged using a filter that passes
a narrow range of wavelengths near the hydrogen Balmer line (right).
The right image is false color,
but similar to the true color of the nebula. The response of the CCD detector is shown below each
image. A comparison of the two images indicates that the emission of light from the nebula is
dominated by H-alpha emission from the gas clouds surrounding the hot central star (bright spot in the
middle).
H-Alpha Emission
The H-alpha emission is being produced by electron recombination of the hydrogen ionized by the hot
central star. The central star is actually a multiple system.
In the H-alpha filter image it is possible to resolve two of the components.
The adjacent right image allows you to turn the filter on and off and watch the nebula morph
from visible light to H-alpha light.
