The Eagle Nebula is another star-forming nebula much like the Orion
Nebula. At 7000 light years away in the constellation of Serpens, it is much
further away than the Orion Nebula. Its alternative name, M16, is its
designation in Charles Messier's catalogue of 1781. Messier compiled a list of
objects in the sky that were 'fuzzy' and extended, unlike the pin-point images
of stars. Objects with an M number (which are nebulae, star clusters or
galaxies) can be seen with a small telescope or binoculars, or even the naked
eye.
These pictures, taken
with WF/PC2 on 1 April 1995, show vast columns of cool, dense gas about a light
year in height. These columns are so dense that the stars within them are
hidden from sight, their light unable to penetrate the gas surrounding them.
The columns are mostly molecular hydrogen, two hydrogen atoms joined together,
which is normally too fragile to exist outside of nebulae. This fragility
arises from the fact that energetic light (such as ultraviolet light) is able
to split the molecules when it hits them. The columns also contain a lot of
microscopic particles mostly made of carbon, known as 'dust', that are able to
form in the protective environment of a nebula.
The columns have such a
strange shape because there are a few very young, massive stars just off the
top of the picture which are 'blowing away' the gas and dust (in the same way
as the Trapezium stars in the Orion Nebula). Their light is breaking up the
molecu-lar hydrogen and heating up the gas in the cloud. When the gas gets
hotter, it starts moving faster and eventually escapes from the nebula. The
less dense parts of the nebula are evap-orated by the stars' radiation first,
leaving behind these columns.
In this image, again, the
colours of the gas indicate which atoms are emitting light in that area. This
time red is sulphur, green is hydrogen and blue is oxygen.