Re: CMBR and neutron stars


"N:dlzc D:aol T:com (dlzc)" <N: dlzc1 D:cox T:net@xxxxxxxxxx> wrote in
message news:TtTKe.19601$E95.19390@xxxxxxxxxxxxx
> Dear Steve Willner:
>
> "Steve Willner" <willner@xxxxxxxxxxxxxxx> wrote in message
> news:42fb9d94$1@xxxxxxxxxxxxxxxxxxxxxxxxxx
>> In article <AvzKe.6008$E95.4317@fed1read01>,
>> "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T:net@xxxxxxxxxx> writes:

>> Let's put in some numbers. The critical density today is about 5E-6
>> protons cm^-2, and baryon density is about 4% of this. So at z=1000,
>> the baryon density was about 200 protons cm^-3. The Thomson
>> scattering cross section is 6.7E-25 cm^2, so optical depth 1 was
>> 7E21 cm or about 1E4 light years, not tens of millions. (I've just
>> done all these calculations in the past few minutes, so it's possible
>> I've made a mistake somewhere. Corrections are welcome.)

The calculation looks right to me (ignoring the
typo? of "cm^-2").

> Google.groups. Thread "Olber's paradox", George Dishman, dated 2003jan05
> <QUOTE>
> This java applet lets you plot the general shape of the
> blackbody curve. Note that it has a clear peak:
>
> http://csep10.phys.utk.edu/guidry/java/planck/planck.html
>
>
> Click new once, then adjust the bottom slider a couple
> of pixels. Repeat that with similar shifts ten times
> representing CBR from a set of 10 shells of stars at some
> large distance. You get a family of overlapping curves and
> if you add the contributions you get a much broader peak.

The above showed qualitatively the broadening you
would get.

> The CMB spectrum follows the blackbody curve to within
> about 1 part in 10^5 which means the source must be a
> thin shell.
> <END QUOTE>

I.e. much thinner.
>
> In later followups, the thickness is estimated.

Indeed, I said:

George Dishman wrote in message avcmdo$mfp$1$8300dec7@xxxxxxxxxxxxxxxx:
> "Jeff Root" <jeff2@xxxxxxxxxxxx> wrote in message
> news:fe58c440.0301052212.4290d481@xxxxxxxxxxxxxxxxxxxxx
> > George Dishman wrote:
> >
> > > The CMB spectrum follows the blackbody curve to within
> > > about 1 part in 10^5 which means the source must be a
> > > thin shell.
> >
> > I don't recall seeing anyone else mention the thickness of
> > the CMBR shell. About fifteen years ago I asked a professor
> > in the astronomy department here, and he said it was about
> > 100 parsecs thick. Does that jibe with your info?
>
> Ouch, I'm not sure. 10^-5 times 13 billion light years is
> about 30 kPc but I think most of the variation is due to
> intrinsic density fluctuations and gravitational effects
> rather than depth variation. ...

So my method was totally incorrect but by
luck I got within an order of magnitude of
Steve's value, tens of thousands of light
years, not tens of millions, though that
is somewhat higher than Jeff's figure.

>> ... As George keeps writing, there is
>> nothing special happening _locally_ at the event horizon.
>
> Now, look at the event horizon form the *inside*. I am proposing that it
> would look *exactly* like the CMBR, without need for Universe filling gas
> and allowing structures right up to the CMBR. *Without* any embarrassing
> questions about how structures could have formed so quickly after having
> been "spread across the Universe".
>
> I'm not trying to wear George down. I hope that is not what I am
> accomplishing...

No, that's ok, but I don't follow why you
are suggesting the event horizon would glow.
It is just a location in an ordinary vacuum.
In another post, you seemed to say it wasn't
the horizon that produced the light but the
stars outside it. Can you be clearer about
what you are proposing.

George


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