Arms
|
The Spiral Arms |
(Section Not Complete)
Astronomical objects often look very different when viewed at different
wavelengths of the
electromagnetic spectrum.
For example, the primary reason
that we perceive spiral galaxies as spirals is that the spiral arms contain
many hot blue and blue-white stars that make these regions more prominent in
the visible spectrum than those regions of the galaxy that are dominated by
older stars whose spectrum is concentrated at longer wavelengths. Here is
an
animation
that illustrates this point. It is a sequence of pictures of the
galaxy
M81
beginnining at ultraviolet wavelengths and progressing through longer
wavelengths to red light.
As the galaxy "morphs" from its UV image to its red light
image, the parts of the galaxy that are visible change considerably.
The initial short wavelength images are dominated by young (less than 1 million
years old) hot stars in the spiral arms; the final long wavelength images are
dominated by old (around
5 billion years) red stars in the core and regions not in the
spiral arms.
Source:
http://zebu.uoregon.edu/movie.html
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