General Relativity Resolves Galactic Rotation Without Exotic Dark Matter

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Everything I need to know I learned through Googling.

Seems odd that a simple, reasonable model would be overlooked for decades. Maybe other investigators just never felt the pressure-free fluid model seemed likely to be the actual way things worked. Maybe people have been scared off by the relativity equations. These guys must be thrilled.
Edit: I skimmed the article. Very interesting. We'll see how this plays out. I'm looking forward to the LHC results. Maybe they will reveal supersymmetric WIMPS.

Hum,

“Their nice fit to observed rotation curves is faked - they are deriving the glactic density from the rotation curves when they should be doing it the other way around.

2) The theory fails to agree with observations near the galactic centre, which is why observations near the galactic centre have all been left off the graphs.

3) The theory fails miserably and irreconcilably when used in modelling the galactic rotation speeds of dwarf galaxies. You will note that none of the figures in the paper are for dwarf galaxies.

4) The use of "General relativity" is not the reason for their good fit. I can get an equally good fit using Newtonian mechanics.”

source


Singular disk of matter in the Cooperstock and Tieu galaxy model
Authors: Mikolaj Korzynski

Recently a new model of galactic gravitational field, based on ordinary General Relativity, has been proposed by Cooperstock and Tieu in which no exotic dark matter is needed to fit the observed rotation curve to a reasonable ordinary matter distribution. We argue that in this model the gravitational field is generated not only by the galaxy matter, but by a thin, singular disk as well. The model should therefore be considered unphysical.

http://arxiv.org/abs/astro-ph/0508377

But apart from that, i like it.

ToSeeked by Brendan Pretty much what I said to Brendan

I'd like to see a galactic computer simulation with GR. It may be more complicated, and it may take a little longer to run, but it seems we have the computes. Cray 1's were used for early simulations, and the box I'm using to post this has 10 times more cycles, and 10 times as much RAM, and its not even a very hot box by today's standards.

This model yields lighter galaxies. How does that affect galaxy clusters?

So, the whole Universe is some 25% less massive. That's some kind of a Universal Weight Loss program.

The Milky Way is nearby. NGC 3031 appears to be M81, a galaxy so bright that there are claims of people seeing it naked eye. NGC 3198 is mag 10.9, NGC 7331 is mag 10.3. I'd guess that the galaxies were chosen as bright, more or less face on galaxies, perhaps with good analysis by others.

Dark Matter seems like an ad hoc solution. Dark Energy is another ad hoc solution. There was a suggested solution to Dark Energy, explained as residual local expansion due to primordial sound waves. With both gone, we're left with just the 5 or 6 percent of the Universe that we've been able to directly detect. I'm not taking any bets, one way or the other, however.

If it were true,
the CBR and background neutrino findings, and the standard theory now need to be tweaked somehow to account for the large scale structures…

<added>
(Another explanation is needed to explain why clusters of galaxies clump together)
</added>

The primordial sound wave theory was discounted because inflation would fatten out the cosmological sized topology too much and it required that we live at the very centre of that trough.

NGC 3031, 3198, and 7331 have inclinations of 64 deg, 74 deg, and 71 deg respectively. This would actually be closer to edge on. Generally, studies of rotation curves are best done for galaxies with inclinations of 30 degrees or greater where 0 deg is face on and 90 deg is edge on.

This is because the observed rotational velocity Vrot is corrected for incl.

Vrot corrected = Vrot obs/sin i

At inclinations closer to 90 deg the effect of the inclination correction is smaller and the uncertainty in the inclination is generally smaller. With inclinations less than 30 degrees the inclinations become very uncertain and the effect of small errors in the estimated inclination become much larger.

They looked at these particular galaxies because they have very well studied rotation curves.

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"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

I don't know if Blob is correct, but I'd wager the original GR result is bunk, and it sounds like Blob has analyzed the reason why. Quite rapidly, it would seem! There are many examples of people getting aphysical results by blindly applying equations, without understanding the ramifications of their own assumptions. Newtonian gravity works fine for all systems with velocities that are way below that of the speed of light, and the last time I checked, that includes the rotation curves of galaxies!