Outside the boundary of the diffusive cosmic-ray halo, the cosmic-ray
flux must drop significantly because (as with photons leaving the
surface of the sun) the cosmic-rays are allowed to stream freely
away from the surface.
A reasonable estimate of the intergalactic cosmic-ray ionization rate
can be obtained by comparing the relative volumes of space and the
relative times spent in each volume, that is,
z
IG
|
~
|
z
CR
( Vhalo / VIG )
( tIG / thalo )
|
|
~
|
z
CR
( 3 x 10-6 )
( 102 )
|
|
~
|
3 x 10-4
z
CR
|
|
~
|
3 x 10-21 s-1
|
If a GMC were introduced to this intergalactic environment,
- its fractional ionization would drop significantly;
- the relevant ambipolar diffusion time would drop below
the free-fall time;
- the cloud may actually be able to cool a little;
- and it ought to be able to make stars like crazy!
Return to: Model Figure
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