Paradoxes Resolved, Origins Illuminated - chandra - dark matter
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rush

74 Posts

Posted - 02 Apr 2008 :  09:49:18  Show Profile  Reply with Quote
It is claimed that the existence of dark matter has been confirmed by CHANDRA in 2006. See the article:

A DIRECT EMPIRICAL PROOF OF THE EXISTENCE OF DARK MATTER
http://arxiv.org/abs/astro-ph/0608407

ABSTRACT
"We present new weak-lensing observations of 1E 0657#8722;558 (), a unique cluster merger, that enable a direct detection of dark matter, independent of assumptions regarding the nature of the gravitational force law. Due to the collision of two clusters, the dissipationless stellar component and the fluid-like X-rayemitting plasma are spatially segregated. By using both wide-field ground-based images and HST/ACS images of the cluster cores, we create gravitational lensing maps showing that the gravitational potential does not trace the plasma distribution, the dominant baryonic mass component, but rather approximately traces the distribution of galaxies. An 8 significance spatial offset of the center of the total mass from the center of the baryonic mass peaks cannot be explained with an alteration of the gravitational force law and thus proves that the majority of the matter in the system is unseen."

It seems that normal matter has been found in an amount not enough to produce the gravitational lensing effect observed.

How modified theory of gravities are taking such observations into account?

Any comments are welcome.

tvanflandern

USA
2793 Posts

Posted - 02 Apr 2008 :  13:30:52  Show Profile  Visit tvanflandern's Homepage  Reply with Quote
quote:
Originally posted by rush

How modified theory of gravities are taking such observations into account?
The study makes a very basic (and common) confusion between gravitational potential effects (such as lensing) and gravitational force effects (such as orbital motion). "Dark matter" is indicated by the behavior of the force law, not by potential distribution. In MM, for example, many lensing effects are refraction in quasar jets and not gravitational in nature at all.

Specifically, the plasma in this pair of clusters would be expected to produce a fairly constant gravitational potential, which yields a zero gravitational force. So it cannot produce much if any lensing because of lack of variation. Galaxies, by contrast, have potential gradients that indicate gravitational forces acting in the usual way, explainable by MOND, MM, and most "dark matter" alternatives. They behave as in any outher single cluster.

The fact that the galaxies produce lensing and the plasma does not is not significant, and the claims in the paper are false. In any fair refereeing process, this paper would never have been published. -|Tom|-
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rush

74 Posts

Posted - 02 Apr 2008 :  16:36:21  Show Profile  Reply with Quote
Tom, do you know any recent peer-reviewed paper that confronts the claims in that paper?
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tvanflandern

USA
2793 Posts

Posted - 02 Apr 2008 :  20:06:22  Show Profile  Visit tvanflandern's Homepage  Reply with Quote
quote:
Originally posted by rush

do you know any recent peer-reviewed paper that confronts the claims in that paper?
No. But is would take a while for one to appear. And prefessional courtesy implies that a wrong paper will be ignored rather than corrected, provided it is doing no harm. (Few scientists are interested in cleaning up the journals. It would be a thankless and never-ending task.) And from a BB perspective, that paper is doing no harm. -|Tom|-
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shando

Canada
205 Posts

Posted - 19 Apr 2012 :  09:28:44  Show Profile  Visit shando's Homepage  Reply with Quote
(Phys.org) -- Serious blow to dark matter theories? New study finds mysterious lack of dark matter in Sun's neighborhood

The most accurate study so far of the motions of stars in the Milky Way has found no evidence for dark matter in a large volume around the Sun. According to widely accepted theories, the solar neighbourhood was expected to be filled with dark matter, a mysterious invisible substance that can only be detected indirectly by the gravitational force it exerts. But a new study by a team of astronomers in Chile has found that these theories just do not fit the observational facts. This may mean that attempts to directly detect dark matter particles on Earth are unlikely to be successful.

from: http://phys.org/news/2012-04-dark-theories-mysterious-lack-sun.html
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Jim

1816 Posts

Posted - 19 Apr 2012 :  12:35:21  Show Profile  Reply with Quote
I read that article the other day. It's amazing how much people will do to discover non-existing stuff. I guess there is no way to change this kind of research without overturning current beliefs somehow.
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