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Physicists Resurrect an Old, Strange Dark Matter Theory
New submitter rossgneumann writes: Dark matter might not be nearly as exotic as most theories suggest. Instead, it could be macroscopic clumps of material formed from common particles already found within the Standard Model of particle physics. This argument comes courtesy of physicists at Case Western University (PDF). Dark matter is usually thought of in terms of exotic, so-far undiscovered particles. The leading candidates are known as weakly interacting massive particles, or WIMPs. But the Case Western theory suggests that there are no dark matter particles, at least none that exist outside of current knowledge. Instead, there are baseball-sized clumps of "regular" matter formed from unexpected combinations of Standard Model particles.
Common particles tend to absorb EMR if they're cold, or emit EMR if they're warm.
I actually RTFP. They specifically mention the density, size and frequency of collision with earth of their posited dark matter candidate.
There was always an assumption that rogue or orphaned planets could contribute. Cross referencing against observations and known theories yielded a contribution that exists, but is far too small. These are what they are refering to as MACHOs.
There needs to be *a lot* of whatever is causing the discrepancies, and that much "normal" matter would probably be easily measured as the effect that the mysterious matter has is significant enough to require an equivalent mass to something like 20-30% of the mass of the universe. It would be difficult to believe we could be off on our observations by that much.
Cold Dark Matter: http://en.wikipedia.org/wiki/C...
MACHOs or Massive Compact Halo Objects are large, condensed objects such as black holes, neutron stars, white dwarfs, very faint stars, or non-luminous objects like planets. The search for these consists of using gravitational lensing to see the effect of these objects on background galaxies. Most experts believe that the constraints from those searches rule out MACHOs as a viable dark matter candidate.[5][6][7][8][9][10]
Also:
http://en.wikipedia.org/wiki/D...
Studies of big bang nucleosynthesis and gravitational lensing have convinced most scientists[10][80][81][82][83][84] that MACHOs of any type cannot be more than a small fraction of the total dark matter.[8][80] Black holes of nearly any mass are ruled out as a primary dark matter constituent by a variety of searches and constraints.[80][82] According to A. Peter: "...the only really plausible dark-matter candidates are new particles."[81]
Yes, it is. We're talking about something that is close in density to neutron-star matter but can exist freely without gravitational confinement of a neutron star. This theory is indeed not new - I've studied it at university as one possible theory for the dark matter. It turns out that if stable clumps of strange matter can exist then it's possible that they form (at least) the bulk of the dark matter. But only barely.
So they would look like baseball or basketball-sized spheres of matter that is even denser than neutronium. It won't be 'dark' - strange particles can interact with photons just fine. These clamps will move at 'galactic' speeds (~100 km/sec) but not at relativistic speeds. They'd be able to punch through the galactic dust clouds like a bullet through a sheet of paper and given the general density of the matter in a galaxies (i.e. 'almost perfect vacuum') the strange clumps are expected to be captured by stars in significant quantities only on the scale of tens of billions of years.
Another interesting feature is their "surface tension" barrier. The strange clumps can NOT accrete normal matter, regular nuclei would simply bounce off the border between the vacuum and the strange matter. This barrier can be pierced by sufficiently energetic individual particles or by slamming into dense matter (i.e. a planet).
The probability of such clump hitting the Earth is about once in every 1000 years. It'll punch through the atmosphere and explode somewhere deep in the crust or in the mantle. From the outside it'd look like a large earthquake.
The various limits on dark matter actually limit the ratio of the scattering cross section and the mass of whatever is making up the dark matter (this obviously does not apply to MOND type theories, which are different).
So, there are two ways to have a more-or-less non-interacting dark matter - have a small mass, and a very, very small cross section (as in WIMPs), or have a large mass, and a high density (as in quark matter DM theories). The large mass means that the scattering cross section can be more or less anything, and, specifically, can be what you would expect for regular matter.
Once the surface tension barrier is breached, the clump explodes in a huge nuclear explosion. Strange matter particles then simply decay and become regular hadrons and form regular nuclei. However, it's also possible that some clumps sank to the core if the collision conditions were just right and surface tension barrier is strong enough.