|Apr30-12, 02:11 PM||#1|
Is the Dark Matter Hypothesis Dead?
Dark matter was introduced in order to make General Relativity (GR) compatible
1. with the rotational speed of galaxies
2. and the relative movement of galaxies in local groups.
A new study has mapped the motions of more than 400 stars up to 13,000 light-years from the Sun. From this new data, they have calculated the mass of material in the vicinity of the Sun, in a volume four times larger than ever considered before.
The amount of mass that we derive matches very well with what we see stars, dust, and gas in the region around the Sun, said Christian Moni Bidin from the University of Concepcion in Chile. But this leaves no room for the extra material dark matter that we were expecting. Our calculations show that it should have shown up very clearly in our measurements. But it was just not there!
Are these results a nail in the coffin of the dark matter hypothesis?
Does it imply that General Relativity is invalid on large spatial scales ?
|Apr30-12, 03:30 PM||#2|
Sean Carroll's take on this:
|Apr30-12, 03:30 PM||#3|
|Apr30-12, 05:19 PM||#4|
Is the Dark Matter Hypothesis Dead?
The galaxy rotation problem is a discrepancy between observed and calculated galaxy rotation curves. The calculations are based on masses derived from the luminosities and assumed mass-to-light ratios in the disk and core portions of spiral galaxies. This discrepancy is currently thought to betray the presence of dark matter that permeates the galaxy and extends into the galaxy's halo.
The Navarro-Frenk-White profile, is often used to model the distribution of mass in dark matter halos. Theoretical dark matter halos produced in computer simulations are best described by the Einasto profile.
So according to the dark matter hypothesis, there is a certain amount of dark matter that should exist in the radius of 13000 light years around the sun based on the dark matter density profile. This was not verified by this study. Dark matter did not show up.
|Apr30-12, 06:30 PM||#5|
It makes you wonder if current density profiles are suspect. It may be possible dark matter is arranged in a sheet like profile aligned with the galactic plane. This would mimic the large scale filament like structures observed in SDSS. It would be interesting to see what a study of stars in the galactic plane would reveal.
|Apr30-12, 08:50 PM||#6|
Bidin & all conclude their paper http://arxiv.org/pdf/1204.3924v1.pdf as follow:
In conclusion, the observations point to a lack of Galactic DM at the solar position, contrary to the expectations of all the current models of Galactic mass distribution. A DM distribution very different to what it is today accepted, such as a highly prolate DM halo, is required to reconcile the results with the DM paradigm. The interpretation of these results is thus not straightforward. We believe that they require further investigation and analysis, both on the observational and the theoretical side, to solve the problems they present. We feel that any attempt to further interpret and explain our results, beyond that presented in this paper, would be highly speculative at this stage. Future surveys, such as GAIA, will likely be crucial to move beyond this point. However, as our results currently stand, we stress that, while numerous experiments seek to directly detect the elusive DM particles, our observations suggest that their density may be negligible in the solar neighborhood. This conclusion does not depend on the cause of this lack of DM at the solar position. For example, if our results are interpreted as evidence of a highly prolate cold DM halo with q ≥2, this would have a local density lower than 2 mM⊙ pc −3
, i.e. more than a factor of four lower than what usually assumed in the interpretation of the results of these experiments.
It is clear that the local surface density measured in our work, extrapolated to the rest of the Galaxy, cannot retain the Sun in a circular orbit at a speed of ∼220 km s −1
. A deep missing mass problem is therefore evidenced by our observations. Indeed, we believe that our results do not solve any problem, but pose important, new ones.
|Apr30-12, 09:02 PM||#7|
The Dark Matter Detection Game in 25 Rhymes, one for each percentage point of our Universe thought to be comprised of it:
When celestial dynamists plot Galaxy rotation curves flatter
Than Kepler demands they invoke dark matter
Although invisible and of unknown substance it does not matter
Theoretical prejudice is promulgated by teachers whose egos matter
Students on the “Standard Bandwagon” propagate the myth of dark matter
To explain Large Scale Structure cosmologists invoke dark matter
Granting it ten times the gravitational importance of ordinary matter
First Cold, then Hot, then Mixed, then biased, what does it matter?
Bandwagon Beliefs are bolstered by the inflation epicycle matter
Invoked to solve the “Flatness problem”, it too needs dark matter
Clusters of galaxies, to remain intact, need dark matter
Otherwise galaxies would fly off and the clusters would shatter
Bending distant starlight needs more than luminous matter
Gravitational lenses too, it is claimed, need dark matter
But how the space-time null geodesic forms is another matter
We are doomed to ignorance unless we settle this matter
And eschew alternate explanations that do matter
Faith in unobservables is what’s the matter
As we learn to eliminate our need for dark matter
Faith in Bandwagon Beliefs will certainly shatter
Lumpy distribution in our galaxy may be another matter
The claim is a Milky Way missing the expected dark matter
Standard Theories may be revised amidst much chatter
And the Searchers, previously thought to be mad as a hatter
Along with their alternative explanations, may suddenly matter
|May1-12, 02:09 PM||#8|
I think there are no current measurements made in the vicinity of any star, including our own Sun, let alone the galactic plane. I'm not sure where or at what altitudes they would be relevant given the variations across the face of a star as well as vertically in its atmosphere; and the plasma physics aspect of stars is not well-enough worked out to give even a theoretical electrical current value for what is observed. If you have the power output, you still need voltage or current to find the remaining variable in the power equation.
It may be a 50 year project to work out the current values required to equal the Sun's measured output, and then confirm it through a comprehensive satellite data monitoring plan at many latitudes and longitudes about the Sun.
Because this is so basic, I think this is a serious fundamental deficiency in our current physics. We may be waiting a long time for the new paradigm...
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