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Number of Stars per Co Moving Unit Volume?



 
 
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  #1  
Old October 10th 16, 01:49 AM posted to sci.astro.research
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Default Number of Stars per Co Moving Unit Volume?

How many stars are there per Gpc^3 Co Moving Volume of the Universe?

I entered numbers into Ned Wright's calculator to find Co Moving
volumes (and radii) for the universe at different z values, in 1Gyr
increments back to 13 Gyrs in the past. I got the following values
using the default settings and "General" button, (which I think
includes the acceleration to the expansion of the universe due to
Dark Energy):

Co
Moving
Volume
Gpc^3
0.134
1.205
4.571
12.252
27.232
53.97
99.348
174.105
296.192
497.486
842.187
1484.868
2997.275 at Universe age - 0.721 Gyrs / z=3D7.368

If there are about 100E9 stars per galaxy and 100E9 galaxies in
universe, do I essentially have

1.0E22 stars per 2997 Gpc^3?

ie, rho_stars ~ 3.34E18 stars / Gpc co moving volume?

So that for each co moving volume above, I can multiply by this
value to get the number of stars within each co moving volume?

Ross
  #2  
Old October 11th 16, 05:42 AM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Posts: 273
Default Number of Stars per Co Moving Unit Volume?

In article ,
writes:

I entered numbers into Ned Wright's calculator to find Co Moving
volumes (and radii) for the universe at different z values, in 1Gyr
increments back to 13 Gyrs in the past. I got the following values
using the default settings and "General" button, (which I think
includes the acceleration to the expansion of the universe due to
Dark Energy):


If there are about 100E9 stars per galaxy and 100E9 galaxies in
universe, do I essentially have

1.0E22 stars per 2997 Gpc^3?

ie, rho_stars ~ 3.34E18 stars / Gpc co moving volume?


Sounds about right.

So that for each co moving volume above, I can multiply by this
value to get the number of stars within each co moving volume?


Roughly, to get the number in such a volume now. Of course, as the
universe expands, matter is conserved, so a given volume has, to zeroth
order, the same number of stars as the universe expands; they just move
farther apart. Of course, galaxies form, stars form, so it is more
complicated.
 




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