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HST and 'dark matter'
Mongo
post Apr 25 2012, 09:26 PM
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Beating an increasingly dead horse here:

Vast Structure of Satellite Galaxies Discovered: Do the Milky Way’s Companions Spell Trouble for Dark Matter?

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Astronomers from the University of Bonn in Germany have discovered a vast structure of satellite galaxies and clusters of stars surrounding our Galaxy, stretching out across a million light years. The work challenges the existence of dark matter, part of the standard model for the evolution of the universe.


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In their effort to understand exactly what surrounds our Galaxy, the scientists used a range of sources from twentieth century photographic plates to images from the robotic telescope of the Sloan Deep Sky Survey. Using all these data they assembled a picture that includes bright 'classical' satellite galaxies, more recently detected fainter satellites and the younger globular clusters.

"Once we had completed our analysis, a new picture of our cosmic neighbourhood emerged," says Pawlowski. The astronomers found that all the different objects are distributed in a plane at right angles to the galactic disk. The newly-discovered structure is huge, extending from as close as 33,000 light years to as far away as one million light years from the centre of the Galaxy.


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The various dark matter models struggle to explain this arrangement. "In the standard theories, the satellite galaxies would have formed as individual objects before being captured by the Milky Way," explains Kroupa. "As they would have come from many directions, it is next to impossible for them to end up distributed in such a thin plane structure."


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Kroupa concludes by highlighting the wider significance of the new work. "Our model appears to rule out the presence of dark matter in the universe, threatening a central pillar of current cosmological theory. We see this as the beginning of a paradigm shift, one that will ultimately lead us to a new understanding of the universe we inhabit."


Link to original article: The VPOS: a vast polar structure of satellite galaxies, globular clusters and streams around the Milky Way

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These findings demonstrate that a near-isotropic infall of cosmological sub-structure components onto the MW is essentially ruled out because a large number of infalling objects would have had to be highly correlated, to a degree not natural for dark matter sub-structures. The majority of satellites, streams and YH GCs had to be formed as a correlated population. This is possible in tidal tails consisting of material expelled from interacting galaxies. We discuss the tidal scenario for the formation of the VPOS, including successes and possible challenges. The potential consequences of the MW satellites being tidal dwarf galaxies are severe. If all the satellite galaxies and YH GCs have been formed in an encounter between the young MW and another gas-rich galaxy about 10-11 Gyr ago, then the MW does not have any luminous dark-matter substructures and the missing satellites problem becomes a catastrophic failure of the standard cosmological model.
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stevesliva
post Apr 26 2012, 02:33 AM
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Does make you wonder if "dark matter" will go the way of planet Vulcan-- explained by a nifty new theory. 'course I've always wondered that.
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Mongo
post Jan 27 2017, 08:31 PM
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The Bullet Cluster as Evidence against Dark Matter

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It might sound like a story from a parallel universe – but it’s true. The Bullet Cluster isn’t the incontrovertible evidence for particle dark matter that you have been told it is. It’s possible to explain the Bullet Cluster with models of modified gravity. And it’s difficult to explain it with particle dark matter.

How come we so rarely read about the difficulties the Bullet Cluster poses for particle dark matter? It’s because the pop sci media doesn’t like anything better than a simple explanation that comes with an image that has “scientific consensus” written all over it. Isn’t it obvious the visible stuff is separated from the center of the gravitational pull?

But modifying gravity works by introducing additional fields that are coupled to gravity. There’s no reason that, in a dynamical system, these fields have to be focused at the same place where the normal matter is. Indeed, one would expect that modified gravity too should have a path dependence that leads to such a delocalization as is observed in this, and other, cluster collisions. And never mind that when they pointed at the image of the Bullet Cluster nobody told you how rarely such an event occurs in models with particle dark matter.
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Gerald
post Jan 28 2017, 03:44 AM
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I'd think, the vast majority of astrophysicists sees it the other way round: Modified Newtonian Dynamics (MOND) and the Bullet Cluster (1E 0657-558)
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We present herein an overview of the theory of MOND and its success at explaining certain observations as well as the Bullet Cluster and its case against MOND

-- I'd think, with MOND we scratch along rule 1.9. Does there exist a peer-reviewed paper supporting the Bullet Cluster ruling out WIMPs?
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fredk
post Jan 28 2017, 06:24 AM
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I agree with Gerald. I'm familiar with the blog post, and somewhat with dark matter. Nonlinear astrophysics is very messy. For gory details and subtleties that the blogger (not a specialist in dark matter) missed check out some of the comments, especially those from Peter Erwin.
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