Miras
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Named after the famous long
period variable Mira. Miras are old stars that have evolved into
so-called asymptotic
giant branch stars. Miras are cooler and much larger
than
the sun. Typically at a late stage of the stars evolution the outer
atmosphere can be blown away so that this phase of the stellar life is
relatively short (tens of thousands of years). Molecules such as SiO
form as the gas condenses. Typically the infrared signature is the sum
of many Planck spectra. In many cases the dust cloud is not think
enough to hide the star. This
combination of a visible star and sum of many Planck distributions
rules out the possibility that such a star is a pure Dyson sphere.
For one explanation of a Miras star see the Harvard-Smithsonian
Miras site.
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OH/IR Maser
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The gas cloud from a Miras star
can give rise to hydoxyl ions (OH) and SiO (silicon monoxide). The dust
formed from silicon monoxide heats up and excites the hydroxyl gving
rise to an inverted population of elevated molecular states. This
inverted population can form a natural maser resulting in very strong
emission at radio frequencies. An OH/IR signal is
evidence against a possible Dyson sphere. For more information
on astronomical masers see the Hartebeesthoek
radio telescope site.
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Protostars and young stars
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Typically star formation occurs
in regions where there is lots of dust such as Orion. A typical
distributions would be the combination of many Planck spectra. This is not the
signature of a pure Dyson sphere.
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Brown dwarfs
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Brown dwarfs are failed stars
with masses less than 0.075 the mass of the sun. This mass is too small
to ignite hydrogen fusion. The heat flux of the Brown Dwarf is due to
the gravitational assembly energy and dissipates over several hundred
million years. Typical temperatures are in the 1000 degree Kelvin
range, too high for normal life. This temperature is higher than most
anticipate for a Dyson Sphere and the luminosity is lower.
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Galaxies
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Characteristically
galaxies detected by the IRAS satellite are relatively nearby and are
not point sources. Even a nearby
Dyson shphere should be a point source in any infrared telescope.
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