Thread: Dark matter is:
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Old November 3rd 17, 04:03 AM posted to sci.astro.research
Steve Willner
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Default Dark matter is:

In article ,
jacobnavia writes:
Why shouldn't [a "sea of galaxies"] be a black body spectrum?

A black body spectrum is the one of a body at thermal equilibrium, and
the sea of galaxies apparently is at thermal equilibrium...


Good grief! Galaxies are nowhere near thermal equilibrium, and their
spectral energy distributions (SEDs) look nothing like blackbodies.
Most galaxy SEDs are double-peaked, and neither peak has a blackbody
SED. And even if galaxies had blackbody SEDs, a sum of blackbodies
at different temperatures (or different redshifts if all galaxies had
the same temperature, which they don't) does not give a blackbody
SED.

Aside from the SED, there's also the matter of the CMB having unit
emissivity, as JT reiterated.

For the CMB, a useful demonstration is at
https://lambda.gsfc.nasa.gov/education/cmb_plotter/
It doesn't allow arbitrary input parameters but shows what the power
spectrum implies.

As to some other points:

I strongly recommend watching the colloquium I posted about earlier.
It explains the current status, contrary to nonsense being posted:
https://youtu.be/pPs_tvDYAl4

I'm curious which observation the "skeptics" think is inconsistent
with the current Big Bang model. (Don't give me "failure to observe
WIMPs," which rules out specific forms of non-baryonic dark matter
but not non-baryonic matter in general. Watch the colloquium for
details.)

That's not to say our current understanding has to be correct.
That's not how science works! However, our current understanding is
consistent with a vast array of observations and inconsistent with
none that I know of.

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