Why is dark matter clumped less densely than matte

newtonian · Jan 16, 2005

The model goes: In the origin of our universe, exotic dark matter clumped before matter because it was not influenced by light (photons) like matter was. Light and matter was linked at first, then eventually light and matter separated. But exotic dark matter clumped first. Therefore, shouldn't it be more densely clumped by now? Or is it more strongly influenced by dark energy than ordinary matter and therefore clumped less densely? The observational evidence for dark matter (exotic or simply dark) in galaxies has it in more distant halos, not near the core - hence less densely clumped.

nexium · Jan 16, 2005

With rare exceptions the subject of exotic dark matter and exotic dark energy are hypothesis rather than theory, so we may have either without the other. When dark matter clumped before light and matter separated; were the clumps mostly nanogram mass or gigaton mass? An important part of the present matter is still in about nanogram clumps. Neil

newtonian · Jan 19, 2005

nexium- Thank you for your response. I would assume the dark matter clumps gradually increased in mass from nanogram to gigaton. My point is that it would seem intuitive that the clumps would be more massive and hence more densely packed than ordinary matter because there was more time for gravitational attraction. Yet the observational evidence for dark matter (perhaps both ordinary like brown dwarfs,etc., and exotic) has most of it beyond most of the matter of our galaxy and other galaxies. My thought is that perhaps exotic dark matter is more influenced by dark energy than ordinary matter is, hence it would not be gravitationally attracted close to the center of gravity. Do you understand my question and possible answer?

newtonian · Jan 23, 2005

Neil, you all - My point: If dark matter is less influenced by gravity and more influenced by dark energy, then it may be disproportionalely distributed beyond our visibility horizon. In that case, not only would its gravitational influence make galaxies rotate faster in outer areas approaching the galactic halo. It would also result in acceleration of expansion due to the gravity of the dark matter beyond our visibility horizon. Do you understand the mechanism I am postulating linking dark matter with accelaration of expansion via the greater influence of dark energy on distant dark matter? Perhaps, in fact, dark energy does not directly influence ordinary matter at all - it may be via the gravity of dark matter which is influenced by dark energy!

newtonian · Jan 29, 2005

Bump! Really - why???? Any ideas out there?

newtonian · Feb 28, 2005

Ok - those of you who prefer me to stay on strictly science, how about responding with a meaningful post? I think it is really important as it may hold the key not only to how structure formed (evolved, was created) in our universe, but also to future expansion.

mooware · Feb 28, 2005

Why is dark matter clumped less densely than matter" Perhaps no one is making a "meaningful post" because currently we don't know why dark matter appears less dense than matter.

Saiph · Mar 1, 2005

well, if the matter clumped into small chunks quickly, it will tend to stay in spherical shapes (like how globular clusters are still spherical), but if it's mostly gaseous (individual particles) it'll flatten into a disk and become more concentrated. Or it could just be less gravitationally inclined... <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newtonian · Mar 1, 2005

mooware - Perhaps. However, questions that have not yet been answered are often of great interest to scientists and those who are scientifically inclined. And the more thinking minds that are pondering over unanswered questions, the more likely someone will hit on a viable theory to consistently explain it within the framework of things already observed and things already proven accurate. To ignore an unanswered question could be to ignore a very important answer that may greatly advance scientific understanding of our universe. In other words: Don't give up just because the question is hard to answer!

newtonian · Mar 1, 2005

Saiph - You lost me! Why would spherical clumps be less dense than disk shaped clumps? Are disk shaped galaxies, like the typical spirals like Milky Way and Andromeda more dense than spherical galaxies?

newtonian · Mar 1, 2005

Saiph - I will research more another day - as I am past my sleep time. However, I couldn't resist a little research: Of spiral galaxies, type Sa have the most tightly wound arms and the largest nuclear regions; type Sb is intermediate, and type Sc have loose, open arms and small nuclei. Spherical galaxies are type E0 [ E zero], i.e. elliptical with zero flattening. And you are probably correct, ellipticals are less massive than spirals so they are likely also less dense. Ellipticals (E0 to E7) range from <1million solar masses to />10 million solar masses. Spirals range from 1 billion to 1 trillion solar masses. However, spherical galaxies have very little net rotation- quite in contrast to the spirals. Which brings up another question - why wouldn't sphericals collapse? Is it dark matter again in an exterior halo? Or are sphericals collapsing and therefore converting to spirals, rather like a figure skater pulling in his (her) arms?

Saiph · Mar 1, 2005

one reason sphericals are less dense is, that for a given mass and radius, they occupy a greater volume as they are spread out in all directions, unlike a disk. The reason existing spheres don't collapse is two-fold. 1) Not much net rotation, so the impetus to collapse into a disk is less. 2) Likely due to rapid formation of large objects (stars basically). The flattening process requires a transfer of momentum from objects in "equatorial" orbits, to the polar ones, via collision. Objects in a polar orbit collide with those in equatorial, and begin rotating in that fashion (moreso anyway). Since there are more objects in equatorial orbits (by definition due to net spin) the polar orbits get depleted, and the equatorial orbits strengthened. This produces a disk shape where objects congregate as much as possible into the equatorial region. However, collisions are required for this process to occur. If large portions of the primordial galaxy formed quickly, into stars, their orbit won't change much. Very rarely are there close enough encounters (let alone collisions) to alter the orbit of an object as large as a star. So rapid formation of stars, means that the galaxies will retain, for longer if not indefinetly, their original shape. This spherical nature can be disturbed by collisions, where you introduce very large density fluctuations, and a huge amount of angular momentum, which can concentrate enough matter that gravity, as opposed to collisions (or very close gravitational relationships) can affect the galaxy. This creates irregulars, which may in time settle into more disk-like shapes, especially if the colliding object was small. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

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