By: Paul Lim and Bear Elders
• Most dense and cold concentrations of interstellar gas
• 0~100K’ degrees cold
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Really dark due to dust particles that extinguishes star lights
There are almost all molecules in these dark clouds
Often times, it’s joined with luminous nebula, forming new stars
Young stars then omit a lot of ultraviolet radiation, lighting up
it’s surrounding area.
• These clouds are even colder than their surroundings (with
temperatures as low as a few tens of kelvins), and thousands or
even millions of times denser.
• These latter clouds are generally called dense interstellar
clouds by researchers, but even these densest interstellar
regions are about as tenuous as the best laboratory vacuum.
• These clouds bear little resemblance to terrestrial clouds. Most
are bigger than our solar system, and some are many parsecs
away.
• Despite the name, these clouds are
made up of primarily gas, just like the
rest of the interstellar medium. However,
their absorption of starlight is due to the
dust they contain.
• These are photos of interstellar
Dust clouds. Pockets of intense
Blackness mark regions where the
Dust and gas are especially
Concentrated and the light from background
Stars is completely obscured.
The bright patches
within the dark region
of dust clouds are
foreground objects,
emission nebulae and
groups of bright stars.
• Astronomers first came to understand exactly what a dust cloud
is around the 1930s due in part by the study of the optical
spectra of distant stars.
• The gas absorbs some radiation depending on its temperature,
density, and elements.
• Because these absorption lines are produced by cold gas,
astronomers can easily detect them from a much broader
spectrum.
• Absorption lines show info about these clouds chemical and
physical makeup.
This simplified diagram
gives us a visual of
interstellar clouds
between a star and
Earth.
The one below it show
the frequency and
intensity of the dust
clouds between the star
and Earth