Dear Mike Dworetsky:

On Wednesday, May 8, 2013 11:58:05 PM UTC-7, Mike Dworetsky wrote:
Yousuf Khan wrote:

If this is true, then it's making it more and
more unnecessary to look for exotic WIMPs and
other such things to explain dark matter, as
dark matter may simply be this invisible gas
between galaxies.

This hypothesis does nothing to address the
problem of dark matter being present in galaxies.
The rotation curves of spiral galaxies, for
example, was one of the first clues that dark
matter exists and does not interact with other
matter except through gravitation.

This has been shown to be an error in the intervening decades. They calibrate the spiral galaxy at its center, assuming it has normal luminosity vs. normal mass distribution, and the Dark Matter component is small. We know this area has a large dark matter collection (the black hole), the area is swept clear, and is abnormally hot (higher luminosity on average than stars near us). The areas further from the center are smaller and cooler, and there is plenty of interstitial dust, so any sort of linear relationship is fatally flawed.

Another clue is in the gravitational lensing of
distant galaxies caused by massive elliptical
galaxies in clusters. There is far more lensing
effect than can be accounted for in the stellar
populations, and ellipticals have very little
interstellar hydrogen.

More bad assumptions. We cannot see the actual stars in the elliptical galaxies, so we SWAG at their populations, and we make the same errors in distributions. Add to this that we expect the "interstellar hydrogen" to be in ground state, but the lion's share of what we are finding is ionized hydrogen and ionized oxygen. Which will be "dark" to optical wavelengths.

It can be simply normal matter, neutrinos, and black holes. We need to look for other options, but it clearly wrong to assume Dark Matter is a fact.

David A. Smith