View Full Version : Properties of Dark Matter
physsist
Sep22-04, 03:45 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n\nHi\nI\'ve been wondering if anyone has looked at the observational\nconstraints on the properties of Dark Matter.\n\nFor example, if Dark Matter had its own equivalent of\nelectromagnetic or nuclear forces, it might be able to form atoms\nwhich could clump together to form massive bodies. We would notice the\ngravitational effects if one of these passed through the earth.\n\nEven if DM particles had no interaction with each other it would\nbe possible for them to be trapped in the gravitational field of the\nearth or moon, giving these bodies an anomalysly large mass.\n\nAnd if they had some interaction with each other we might observe\nmysterious increases or decreases in the masses of celestial bodies.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Hi
I've been wondering if anyone has looked at the observational
constraints on the properties of Dark Matter.
For example, if Dark Matter had its own equivalent of
electromagnetic or nuclear forces, it might be able to form atoms
which could clump together to form massive bodies. We would notice the
gravitational effects if one of these passed through the earth.
Even if DM particles had no interaction with each other it would
be possible for them to be trapped in the gravitational field of the
earth or moon, giving these bodies an anomalysly large mass.
And if they had some interaction with each other we might observe
mysterious increases or decreases in the masses of celestial bodies.
Uncle Al
Sep23-04, 04:46 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nphyssist wrote:\n>\n> Hi\n> I\'ve been wondering if anyone has looked at the observational\n> constraints on the properties of Dark Matter.\n>\n> For example, if Dark Matter had its own equivalent of\n> electromagnetic or nuclear forces, it might be able to form atoms\n> which could clump together to form massive bodies. We would notice the\n> gravitational effects if one of these passed through the earth.\n>\n> Even if DM particles had no interaction with each other it would\n> be possible for them to be trapped in the gravitational field of the\n> earth or moon, giving these bodies an anomalysly large mass.\n>\n> And if they had some interaction with each other we might observe\n> mysterious increases or decreases in the masses of celestial bodies.\n\nhttp://arxiv.org/abs/astro-ph/0403292\nhttp://arXiv.org/abs/astro-ph/0310723\nWMAP + Sloane Digital Sky Survey\nhttp://arxiv.org/abs/hep-ph/0404175\nDark matter candidates\n<http://nedwww.ipac.caltech.edu/level5/March01/Carroll/frames.html>\nCarroll on what it all means.\n\nDark matter must have no electromagnetic, Strong, or Weak interactions\nat all with ordinary matter (e.g., scattering) or photons or it would\nbe screamingly detectable. Dark matter must be gravitationally bound\nonly and have no binding or other interactions with itself (e.g.,\ncooling by radiation emission) or it would not form the uniform\nspherical distribution necessary to curve fit visible matter\ndistribution in spiral galaxies persistent over all visible time\n(large red shifts).\n\nA suitable dark matter candidate would be the neutralino that is\nsafely undetectable even in principle. Theory that cannot be\nempirically challenged is weak.\n\n--\nUncle Al\nhttp://www.mazepath.com/uncleal/\n(Toxic URL! Unsafe for children and most mammals)\nhttp://www.mazepath.com/uncleal/qz.pdf\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>physsist wrote:
>
> Hi
> I've been wondering if anyone has looked at the observational
> constraints on the properties of Dark Matter.
>
> For example, if Dark Matter had its own equivalent of
> electromagnetic or nuclear forces, it might be able to form atoms
> which could clump together to form massive bodies. We would notice the
> gravitational effects if one of these passed through the earth.
>
> Even if DM particles had no interaction with each other it would
> be possible for them to be trapped in the gravitational field of the
> earth or moon, giving these bodies an anomalysly large mass.
>
> And if they had some interaction with each other we might observe
> mysterious increases or decreases in the masses of celestial bodies.
http://arxiv.org/abs/http://www.arxiv.org/abs/astro-ph/0403292
http://arXiv.org/abs/http://www.arxiv.org/abs/astro-ph/0310723
WMAP + Sloane Digital Sky Survey
http://arxiv.org/abs/http://www.arxiv.org/abs/hep-ph/0404175
Dark matter candidates
<http://nedwww.ipac.caltech.edu/level5/March01/Carroll/frames.html>
Carroll on what it all means.
Dark matter must have no electromagnetic, Strong, or Weak interactions
at all with ordinary matter (e.g., scattering) or photons or it would
be screamingly detectable. Dark matter must be gravitationally bound
only and have no binding or other interactions with itself (e.g.,
cooling by radiation emission) or it would not form the uniform
spherical distribution necessary to curve fit visible matter
distribution in spiral galaxies persistent over all visible time
(large red shifts).
A suitable dark matter candidate would be the neutralino that is
safely undetectable even in principle. Theory that cannot be
empirically challenged is weak.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
Ilja Schmelzer
Sep24-04, 08:12 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"physsist" <physsist@volcanomail.com> schrieb\n> I\'ve been wondering if anyone has looked at the observational\n> constraints on the properties of Dark Matter.\n\nOf course.\n\nObservational constraints have been used to distinguish even several\ntypes of dark matter.\n\nFirst, there is so-called cold dark matter (CDM). It behaves like\ndust of particles with nonzero mass. It is concentrated around\ngalaxies.\n\nThen, it is known that CDM alone is not sufficient. There is another\ncomponent which seems homogeneous and does not fit into the\nproperties of usual matter. It behaves like something with negative\npressure.\n\n> Even if DM particles had no interaction with each other it would\n> be possible for them to be trapped in the gravitational field of the\n> earth or moon, giving these bodies an anomalysly large mass.\n\nThis is approximately what happens with galaxies.\n\nIlja\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"physsist" <physsist@volcanomail.com> schrieb
> I've been wondering if anyone has looked at the observational
> constraints on the properties of Dark Matter.
Of course.
Observational constraints have been used to distinguish even several
types of dark matter.
First, there is so-called cold dark matter (CDM). It behaves like
dust of particles with nonzero mass. It is concentrated around
galaxies.
Then, it is known that CDM alone is not sufficient. There is another
component which seems homogeneous and does not fit into the
properties of usual matter. It behaves like something with negative
pressure.
> Even if DM particles had no interaction with each other it would
> be possible for them to be trapped in the gravitational field of the
> earth or moon, giving these bodies an anomalysly large mass.
This is approximately what happens with galaxies.
Ilja
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>>\n> http://arxiv.org/abs/astro-ph/0403292\n> http://arXiv.org/abs/astro-ph/0310723\n> WMAP + Sloane Digital Sky Survey\n> http://arxiv.org/abs/hep-ph/0404175\n> Dark matter candidates\n> <http://nedwww.ipac.caltech.edu/level5/March01/Carroll/frames.html>\n> Carroll on what it all means.\n>\n> Dark matter must have no electromagnetic, Strong, or Weak interactions\n> at all with ordinary matter (e.g., scattering) or photons or it would\n> be screamingly detectable.\n\nthat\'s not quite right. the most promising cold dark matter candidate " WIMP"\nis expected to have wek-scale interactions with ordinary matter. Of course that\ndoes not mean that teh cold dark matter is a WIMP. It coould be something\nmore exotic, Also I have see papers in literature about dark matter being SIMPs\n(strongly interacting massive particles).\n\nMelroy\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>>
> http://arxiv.org/abs/http://www.arxiv.org/abs/astro-ph/0403292
> http://arXiv.org/abs/http://www.arxiv.org/abs/astro-ph/0310723
> WMAP + Sloane Digital Sky Survey
> http://arxiv.org/abs/http://www.arxiv.org/abs/hep-ph/0404175
> Dark matter candidates
> <http://nedwww.ipac.caltech.edu/level5/March01/Carroll/frames.html>
> Carroll on what it all means.
>
> Dark matter must have no electromagnetic, Strong, or Weak interactions
> at all with ordinary matter (e.g., scattering) or photons or it would
> be screamingly detectable.
that's not quite right. the most promising cold dark matter candidate " WIMP"
is expected to have wek-scale interactions with ordinary matter. Of course that
does not mean that teh cold dark matter is a WIMP. It coould be something
more exotic, Also I have see papers in literature about dark matter being SIMPs
(strongly interacting massive particles).
Melroy
mathman
Sep28-04, 02:26 AM
This description is not mine. I am a (retired) mathematician, and all this physics is stuff I pick up, mostly from ArXiv. If you want to get a fuller description look for any recent articles by Michael Turner, such as in ArXiv.
TillEulenspiegel
Sep28-04, 02:26 AM
Um sorry guys, You have a completely incorrect idea of dark matter.
Dark matter is a broad stroke of the semantical brush that includes everything from particulate matter in vacuum space to planets we cannot directly observe to super massive dark bodies, to WIMPS and MACHOS , to black holes where the only observation that is available is it's effect on the matter around it . It is not DE or any exotic creature postulated by the latest version of string or brane theory only matter that SHOULD exist because of the way galaxies and local systems behave. There are alternative paths available to explain these realities but the situation is that there is a quantity that should make up 90% more of the matter that we directly observe to explain the behavior of the universe and we don't know what it is .
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