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Copernicus
2012-Sep-05, 12:51 AM
In the following article proposes a theory for dark matter. http://phys.org/news/2012-09-mystery-dark-deciphered.html

To me it seems to be a preposterous idea because the dark matter only orbits the galaxies black holes, but for some reason solar systems don't need any dark matter.

What do other people think?

Cougar
2012-Sep-05, 02:23 AM
...the following article proposes a theory for dark matter. http://phys.org/news/2012-09-mystery-dark-deciphered.html

The corresponding recent paper (http://arxiv.org/abs/1208.5483) is not so certain:


Subsequently, there has been significant theoretical interest in determining the origin of the very hard spectrum of progenitor electrons. Suggestions include enhanced supernova rates (Biermann et al. 2010), a Galactic wind (Crocker & Aharonian 2011), a jet generated by accretion onto the central black hole (Guo & Mathews 2011; Guo et al. 2011), and co-annihilation of dark matter (DM) particles in the Galactic halo (Finkbeiner 2004b; Hooper et al. 2007; Lin et al. 2010; Dobler et al. 2011). However, while each of these scenarios can reproduce some of the properties of the haze/bubbles well, none can completely match all of the observed
characteristics (Dobler 2012).

Shaula
2012-Sep-05, 05:58 AM
It doesn't say that DM is only around the centre of the SMBH, just that this is the only place where its density is high enough to produce a detectable signal.

Personally I think it is a weak series of speculations based on little or no theory. But I may be wrong.

Copernicus
2012-Sep-05, 08:44 AM
It doesn't say that DM is only around the centre of the SMBH, just that this is the only place where its density is high enough to produce a detectable signal.

Personally I think it is a weak series of speculations based on little or no theory. But I may be wrong.

Hi Shaula,

I know they didn't say that, but it is the galaxies velocity profile that is off my a mass and distribution of mass by a factor of 10. There doesn't appear to be a problem with the velocity curves of solar systems.

antoniseb
2012-Sep-05, 10:35 AM
... it is the galaxies velocity profile that is off my a mass and distribution of mass by a factor of 10. There doesn't appear to be a problem with the velocity curves of solar systems.
The basic idea is that Dark Matter formed collections roughly the spatial size of small galaxies, and can never really cool off enough to shrink. The Solar System is much too small to have collected significant amounts of Dark Matter.

Cougar
2012-Sep-05, 12:23 PM
...it is the galaxies velocity profile that is off my a mass and distribution of mass by a factor of 10. There doesn't appear to be a problem with the velocity curves of solar systems.

Yeah, but the radius of the solar system is about 4 ten-thousandths of a lightyear, while the radius of the galaxy is 50,000 lightyears. The galaxy is 90 billion times bigger, and you're puzzled over "a factor of 10"?

Shaula
2012-Sep-05, 01:33 PM
Hi Shaula,

I know they didn't say that, but it is the galaxies velocity profile that is off my a mass and distribution of mass by a factor of 10. There doesn't appear to be a problem with the velocity curves of solar systems.
Nor is the Solar system's rotation curve expected to be. As other posters have covered, standard dark matter models do not allow clumping at such small scales in a reasonable timescale or in the environment the Sun is in. Your comment is a little like saying there is a problem with the existence of Neptunebecause we see evidence of its orbital perturbations on Uranus but not on a GPS satellite.

Copernicus
2012-Sep-05, 02:13 PM
Why wouldn't solar systems capture this dark matter? It should be all around us? I realize that the dark matter models would not allow clumping. They couldn't, otherwise the model wouldn't fit the data. I worked in manufacturing and healthcare many years. People always find convenient ways to model their work universe to their own philosophy. When you are an employee, when the boss says jump, you say how high. Resistance is futile, you will comply.

antoniseb
2012-Sep-05, 02:36 PM
Some dark matter could be captured by the solar system, but it would be a negligible amount. Each Dark Matter particle is an independent object sailing passed the Sun at perhaps 400 kilometers/second. After a lucky combinations of interactions with massive objects *some* dark matter particles will slow down, and a sufficiently slow one on the right trajectory might get captured by a interactions with the Sun and Jupiter. The circumstances that would let this happen are very rare, and can mostly be discounted for macroscopic observations.

Copernicus
2012-Sep-05, 02:57 PM
What are the odds it would get captured by a galaxy? Who has done the calculations? Why is it so perfectly uniform in a galaxy to give a flat velocity curve to galaxies?

Thanks in advance.

Shaula
2012-Sep-05, 04:10 PM
What are the odds it would get captured by a galaxy?
Very good - the CDM models imply that it is slow moving and largely collisionless. So clustering on very large scales is possible


Who has done the calculations?
Huge numbers of people have calculated, modelled and worked on this. Literally thousands. Any reference site will start you off on this, or try arxiv. This question is rather like asking who has ever modelled planetary orbits in the 1800s.


Why is it so perfectly uniform in a galaxy to give a flat velocity curve to galaxies?
Because it doesn't easily clump and the spherical halo is much, much larger than the galaxy. The stars are embedded in a much larger structure so to the limits of our measurements their rotation curves flatten. It is pretty well established in modelling circles how to simulate this.

I don't want to pretend that there are no unanswered questions, there are a lot of possible tweaks to the models and descriptions we use. But these basic questions have long ago been worked out. Wikipedia has a summary and links to other pages.


Why wouldn't solar systems capture this dark matter?
Because the dark matter is cool but hard to cool, so it tends to escape over small scales. We may attract it but we cannot hold on to it very well. So the density gradient around the solar system is very, very small.


They couldn't, otherwise the model wouldn't fit the data.
Yes, that is how models work - you adjust them to fit evidence available and throw them out if a better one comes along. So far no better one has come along.


People always find convenient ways to model their work universe to their own philosophy. When you are an employee, when the boss says jump, you say how high. Resistance is futile, you will comply.
Yes and science is full of eager and keen young researchers looking to unseat the old school and be part of a revolution in physics. Trouble is there is a lot of evidence for the current models. Challenging the mainstream is encouraged, not just tolerated. And so far dark matter remains the best solution to observations.

Swift
2012-Sep-05, 05:52 PM
I worked in manufacturing and healthcare many years. People always find convenient ways to model their work universe to their own philosophy. When you are an employee, when the boss says jump, you say how high. Resistance is futile, you will comply.
Copernicus,

I'm a little unclear what your point is here. It almost sounds like you are advocating some conspiracy or deliberate action among astronomers to force some unfounded beliefs on others. If that is your point, you need to drop it right now, or you will be infracted for advocating non-mainstream ideas in Q&A. Q&A is for asking questions and getting mainstream answers. If you don't like those answers, take your debate to ATM. But then you know that.

antoniseb
2012-Sep-05, 06:40 PM
What are the odds it would get captured by a galaxy? Who has done the calculations? Why is it so perfectly uniform in a galaxy to give a flat velocity curve to galaxies?
I like Shaula's answers but I'm giving slightly different nuances of the same answers:

What are the odds it would get captured by a galaxy? Actually collectively, the dark matter particles captured the baryonic parts of the galaxy, not the other way around.
Who did the calculations? See Shaula's answer, it's great.
Perfectly uniform to give flat rotation curves? I don't like your use of the word "perfectly" here. The rotation curves are not flat, they are approximately flat, and the dark matter distribution is not completely uniform, but it is much more smoothly distributed than is baryonic matter.