No Need For Dark Matter To Explain Rotation Of Spiral Galaxies, Says Italian Mathematician
By on December 5th, 2011

The Universe may not be as dark as previously thought, if an Italian mathematician is to be believed. A. Carati, an Italian mathematician, has made a bold proposition if faraway matteris allowed to interact with galactic matter, it can be shown that their gravitational effects reproduce the galactic rotational curves extremely faithfully! This rules out the need for any non-luminous, or dark, matter.

The Inception of Dark Matter

The problem of dark matter in case of galactic rotation curves is stated as follows. Astronomers have made theoretical predictions (using Einstein’s General Relativity) about the speed of the different parts of the galaxy and their distance from the center. When the velocity is plotted against distance, what we get is called a velocity curve. The problem is that while you expect a certain curve given the amount of luminous matter in a galaxy, what is directly observed is that the velocity curve deviates significantly from this, especially as one goes away from the center. Astrophysicists invoked the presence of dark matter’ or non-luminous matter to save Einstein’s gravitational theory.

This is what a typical curve looks like.

A typical rotation curve for a spiral galaxy. The red line is the theoretical prediction - called the Keplerian case. (The dots represent some data and the green line interpolates the data.)

Enter the mathematician

Now, what Carati claims is that if faraway matter is allowed to exert gravitational forces, which, of course, it does, then the rotation curves for spiral galaxies can be explained away. The effect of matter in faraway galaxies is generally neglected in all calculations, since the galaxies are assumed to be uniformly distributed throughout the Universe. (This is the principle of isotropy in space, which is a guiding principle for Cosmology.)

The idea that galaxies might be arranged according to a very complex fractal structure was originated by Sylos Labini in 1998. Carati took up from this point, and making a few simplifying assumptions about the de-correlation of matter at large distances, he showed that the forces that this matter might exert is of the order of 0.2 cH0, H0 being the Hubble’s constant.

The crucial point is that this force is good enough to explain the anomalous rotation curves! And the fit is amazingly accurate.

If seeing is believing, or, at least, suspending disbelief we present the rotation curves for two spiral galaxies NGC 3198 and NGC 2403. Look at the expected curve and how well the observed points fit it!

Rotation Curve for NGC 3198. Look at the amazing fit! (Data obtained from HII data)

The rotation curve for NGC 2403. (Triangles are HI data and squares are HII data)

True, this is an outlandish idea, but so is dark matter. The fact that General Relativity can produce such stunning verification of the experimental data is quite satisfying.

We don’t have any word on how this will solve many of the other puzzles that dark matter solves, mainly the Cosmic Background radiation distribution (WMAP data) and the observed gravitational lensing effects.

A.Carati presents his paper here:  http://arxiv.org/PS_cache/arxiv/pdf/1111/1111.5793v1.pdf
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Author: Debjyoti Bardhan Google Profile for Debjyoti Bardhan
Is a science geek, currently pursuing some sort of a degree (called a PhD) in Physics at TIFR, Mumbai. An enthusiastic but useless amateur photographer, his most favourite activity is simply lazing around. He is interested in all things interesting and scientific.

Debjyoti Bardhan has written and can be contacted at debjyoti@techie-buzz.com.
 
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