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#1
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Can dark matter be small objects?
Gas and dust is able to be detected by its effect on light. Large
objects glow from their own light. If intermediate objects were at low temperature would they generally be detectable? There are many orders of magnitude between dust and the dimmest starts. How many of these could definitely not contribute to dark matter and why? [[Mod. note -- It's almost impossible to say that something does "definitely not contribute"; usually "all" we can do is put upper limits on any possible contribution. Gravitational-lensing observations are often used to place such limits, and we've discussed them numerous times in this newsgroups. -- jt]] |
#2
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Can dark matter be small objects?
In article , Ray
Tomes writes: Gas and dust is able to be detected by its effect on light. Large objects glow from their own light. If intermediate objects were at low temperature would they generally be detectable? There are many orders of magnitude between dust and the dimmest starts. How many of these could definitely not contribute to dark matter and why? "Dark matter" is a bit of a misnomer. What most people mean these days is "some sort of non-baryonic matter, other than neutrinos, which we have not yet detected". This is the "DM" in, e.g., "LambdaCDM". Other things can be dark, such as cold gas, dust, and so on. However, we have good upper (and lower) limits on baryons from big-bang nucleosynthesis, so while there are some dark baryons, they cannot be an appreciable fraction of the dark matter. It's also a bit of a misnomer since "dark" here means that it does not interact electromagnetically. Yes, that means it doesn't glow, but it also means that it doesn't reflect or absorb light. In other words, it is transparent. At most it is weakly interacting (i.e. via the weak "nuclear" force), but this is not something which can be investigated astrophysically, so only gravitational effects are left. (Since we don't know what it is, we don't know if it is self-interacting and hence don't know if it can form macroscopic objects.) |
#3
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Can dark matter be small objects?
On 4/19/2015 11:24 PM, Phillip Helbig (undress to reply) wrote:
In article , Ray Tomes writes: Gas and dust is able to be detected by its effect on light. Large objects glow from their own light. If intermediate objects were at low temperature would they generally be detectable? There are many orders of magnitude between dust and the dimmest starts. How many of these could definitely not contribute to dark matter and why? "Dark matter" is a bit of a misnomer. What most people mean these days is "some sort of non-baryonic matter, other than neutrinos, which we have not yet detected". This is the "DM" in, e.g., "LambdaCDM". Other things can be dark, such as cold gas, dust, and so on. However, we have good upper (and lower) limits on baryons from big-bang nucleosynthesis, so while there are some dark baryons, they cannot be an appreciable fraction of the dark matter. It's also a bit of a misnomer since "dark" here means that it does not interact electromagnetically. Yes, that means it doesn't glow, but it also means that it doesn't reflect or absorb light. In other words, it is transparent. At most it is weakly interacting (i.e. via the weak "nuclear" force), but this is not something which can be investigated astrophysically, so only gravitational effects are left. (Since we don't know what it is, we don't know if it is self-interacting and hence don't know if it can form macroscopic objects.) Why is it that gravitational interacting is always mentioned separately? Why not say: At most it is weakly interacting (i.e. via the weak "nuclear" and gravitational forces). [[Mod. note -- The reason is that the weak (nuclear) interaction is a "short-range" force -- its strength drops exponentially with distance, so it's utterly negligible for astronomical distances. Gravitation, in contrast, is a "long-range" force, with (approximately) a 1/r^2 falloff with distance, so it can still be substantial at astronomical distances. -- jt]] |
#4
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Can dark matter be small objects?
On 4/19/15 11:24 PM, Phillip Helbig (undress to reply) wrote:
In article , Ray Tomes writes: Gas and dust is able to be detected by its effect on light. Large objects glow from their own light. If intermediate objects were at low temperature would they generally be detectable? There are many orders of magnitude between dust and the dimmest starts. How many of these could definitely not contribute to dark matter and why? "Dark matter" is a bit of a misnomer. What most people mean these days is "some sort of non-baryonic matter, other than neutrinos, which we have not yet detected". This is the "DM" in, e.g., "LambdaCDM". Other things can be dark, such as cold gas, dust, and so on. However, we have good upper (and lower) limits on baryons from big-bang nucleosynthesis, so while there are some dark baryons, they cannot be an appreciable fraction of the dark matter. There is a question as to whether the "good upper (and lower) limits on baryons from big-bang nucleosynthesis" must be modified by high Z 'gold' collision experiments conducted inside the Relativistic Heavy Ion Collider (RHIC), an atom smasher at Brookhaven National Laboratory in Upton, New York. Hints of Mysterious Particle Detected in 'Big Bang Soup' http://www.livescience.com/47506-hea...ons-found.html http://www.bnl.gov/rhic/news2/news.asp?a=4473&t=today https://www.quantamagazine.org/20150...lider-awakens/ As established in physical chemistry, reaction rates change in solvents 'Big Bang Soup Z1' vs gaseous 'particle Z=1 ' phase. It's also a bit of a misnomer since "dark" here means that it does not interact electromagnetically. Yes, that means it doesn't glow, In order for it not to glow, it must be extremely cold and if it were baryonic matter, how cold would that be? but it also means that it doesn't reflect or absorb light. In other words, it is transparent. If dark matter objects had size dimensions on the order of meters, then the dark matter galactic density on the order of 10^-24 g/cc composed of these objects would have a mean free path or optical density such that they would not be optically visible under current methods or in other words these dark matter objects would in aggregate be observationally transparent in accordance with Beer Lambert Law http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law At most it is weakly interacting (i.e. via the weak "nuclear" force), but this is not something which can be investigated astrophysically, so only gravitational effects are left. (Since we don't know what it is, we don't know if it is self-interacting and hence don't know if it can form macroscopic objects.) The WIMP approach seems to be a dead end based on negative experimental results from the many current underground scintillation experiments. Richard D Saam |
#5
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Can dark matter be small objects?
Phillip Helbig (undress to reply) wrote:
In article , Ray Tomes writes: Gas and dust is able to be detected by its effect on light. Large objects glow from their own light. If intermediate objects were at low temperature would they generally be detectable? There are many orders of magnitude between dust and the dimmest starts. How many of these could definitely not contribute to dark matter and why? "Dark matter" is a bit of a misnomer. What most people mean these days is "some sort of non-baryonic matter, other than neutrinos, which we have not yet detected". This is the "DM" in, e.g., "LambdaCDM". Other things can be dark, such as cold gas, dust, and so on. However, we have good upper (and lower) limits on baryons from big-bang nucleosynthesis, so while there are some dark baryons, they cannot be an appreciable fraction of the dark matter. It's also a bit of a misnomer since "dark" here means that it does not interact electromagnetically. Yes, that means it doesn't glow, but it also means that it doesn't reflect or absorb light. In other words, it is transparent. At most it is weakly interacting (i.e. via the weak "nuclear" force), but this is not something which can be investigated astrophysically, so only gravitational effects are left. (Since we don't know what it is, we don't know if it is self-interacting and hence don't know if it can form macroscopic objects.) What intrigues me about DM is that beyond some point from the galactic center the sum of luminous and dark matter, as a function of r, is constant. Just how far out does that hold? Could this constancy be a result of galactic formation or could it be true everywhere? Could DM be proto baryonic matter? |
#6
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Can dark matter be small objects?
root wrote:
Phillip Helbig (undress to reply) wrote: In article , Ray Tomes writes: Gas and dust is able to be detected by its effect on light. Large objects glow from their own light. If intermediate objects were at low temperature would they generally be detectable? There are many orders of magnitude between dust and the dimmest starts. How many of these could definitely not contribute to dark matter and why? "Dark matter" is a bit of a misnomer. What most people mean these days is "some sort of non-baryonic matter, other than neutrinos, which we have not yet detected". This is the "DM" in, e.g., "LambdaCDM". Other things can be dark, such as cold gas, dust, and so on. However, we have good upper (and lower) limits on baryons from big-bang nucleosynthesis, so while there are some dark baryons, they cannot be an appreciable fraction of the dark matter. It's also a bit of a misnomer since "dark" here means that it does not interact electromagnetically. Yes, that means it doesn't glow, but it also means that it doesn't reflect or absorb light. In other words, it is transparent. At most it is weakly interacting (i.e. via the weak "nuclear" force), but this is not something which can be investigated astrophysically, so only gravitational effects are left. (Since we don't know what it is, we don't know if it is self-interacting and hence don't know if it can form macroscopic objects.) What intrigues me about DM is that beyond some point from the galactic center the sum of luminous and dark matter, as a function of r, is constant. Just how far out does that hold? Could this constancy be a result of galactic formation or could it be true everywhere? I was hoping the moderator would have dropped my post above. Rather than saying the sum of luminous and dark matter is constant, I should have said that it is only a function of r. Could DM be proto baryonic matter? |
#7
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Can dark matter be small objects?
In article , "Richard D.
Saam" writes: There is a question as to whether the "good upper (and lower) limits on baryons from big-bang nucleosynthesis" must be modified by high Z 'gold' collision experiments conducted inside the Relativistic Heavy Ion Collider (RHIC), an atom smasher at Brookhaven National Laboratory in Upton, New York. Is there any evidence that this is relevant to BBN? In order for it not to glow, it must be extremely cold and if it were baryonic matter, how cold would that be? Anything above absolute zero emits radiation. You can calculate the intensity as a function of wavelength from the temperature (under certain assumptions). If dark matter objects had size dimensions on the order of meters, then the dark matter galactic density on the order of 10^-24 g/cc composed of these objects would have a mean free path or optical density such that they would not be optically visible under current methods Right: back issue of the ApJ, or bricks. :-) Right, we don't know whether it consists of microscopic objects, but if so, presumably it would have to be self-interacting with a cross section much larger than for the weak interaction. The WIMP approach seems to be a dead end based on negative experimental results from the many current underground scintillation experiments. Absence of evidence is not evidence of absence. Many particles were predicted and discovered only years or decades later. In the case of dark matter, it is not even clear what properties it must have, or at least the range is much larger, so it is not easy to say where to look. |
#8
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Can dark matter be small objects?
In article , "Phillip Helbig (undress to
reply)" writes: Right: back issue of the ApJ, or bricks. :-) Right, we don't know whether it consists of microscopic objects, but if so, presumably it would have to be self-interacting with a cross section much larger than for the weak interaction. Microscopic --- macroscopic. If it consists of macroscopic objects, they have to be held together, which implies some sort of self-interaction. (The self-interaction could be gravity, but if gravity is the only force involved, it is more difficult to form objects, since accretion is efficient only after a certain mass has been reached, and in order to reach this, one needs some other mechanism to make bits of the object stick together and/or some mechanism for cooling. Black holes are possible, but have been ruled out observationally in many mass ranges.) |
#9
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Can dark matter be small objects?
[[Mod. note -- Note that arXiv:1503.07675 does NOT claim to have detected
a nonzero self-interaction cross section of dark matter. Rather, it claims to have place an *upper limit* on any such cross section. -- jt]] On 4/23/15 7:46 PM, Phillip Helbig (undress to reply) wrote: In article , "Richard D. Saam" writes: There is a question as to whether the "good upper (and lower) limits on baryons from big-bang nucleosynthesis" must be modified by high Z 'gold' collision experiments conducted inside the Relativistic Heavy Ion Collider (RHIC), an atom smasher at Brookhaven National Laboratory in Upton, New York. Is there any evidence that this is relevant to BBN? Current BBN simulation reactions predict universe H, He, Li? gaseous abundances but this does not negate the possibility of another BBN reaction phase (liquid, solid and/or other) as experimentally observed by RHIC resulting in DM baryonic hydrogen phase not observed in Baryonic Acoustic Oscillations and cold so as not to glow and such object size as to be transparent in aggregate. In order for it not to glow, it must be extremely cold and if it were baryonic matter, how cold would that be? Anything above absolute zero emits radiation. You can calculate the intensity as a function of wavelength from the temperature (under certain assumptions). DM object thermal emissivity may be an indicator of these low temperatures although related extremely long wavelengths are not measurable at this time as calculated by established black body spectrum peak wave length theory. wave length (cm) = h*c/(4.96536456*Boltzmann*T) Emission T K Emission wave length (cm) 2.2E+01 1.3E-02 2.7E+00 1.1E-01 1.0E+00 2.9E-01 1.0E-01 2.9E+00 1.0E-02 2.9E+01 1.0E-03 2.9E+02 1.0E-04 2.9E+03 1.0E-05 2.9E+04 1.0E-06 2.9E+05 1.0E-07 2.9E+06 1.0E-08 2.9E+07 1.0E-09 2.9E+08 1.0E-10 2.9E+09 1.0E-11 2.9E+10 1.0E-12 2.9E+11 1.0E-13 2.9E+12 1.0E-14 2.9E+13 1.0E-15 2.9E+14 1.0E-16 2.9E+15 1.0E-17 2.9E+16 So the secondary phase DM could be there and at a temperature CMBR 2.7K and not in thermal equilibrium with measured universe gaseous H, He Li? and currently not thermally measurable. If dark matter objects had size dimensions on the order of meters, then the dark matter galactic density on the order of 10^-24 g/cc composed of these objects would have a mean free path or optical density such that they would not be optically visible under current methods Right: back issue of the ApJ, or bricks. :-) Right, we don't know whether it consists of microscopic objects, but if so, presumably it would have to be self-interacting with a cross section much larger than for the weak interaction. and what is the accepted weak interaction cross-section? This reference http://arxiv.org/abs/1503.07675 indicates dark matter cross-section and resultant drag characteristics for 72 studied galactic collisions 0.47 cm^2/g This cross-section can be interpreted as objects of ~meter size and density ~1 g/cc If the context of the red, blue and green dots in http://arxiv.org/abs/1503.07675 Figure 1, the represented entities could be interpreted as being separated in accordance with cross-section gas 5E7 cm^2/g (calculated atom area/mass) dark matter 0.47 cm^2/g stars 7E-12 cm^2/g (calculated sun area/mass) with the hydrodynamic mechanism (with a drag coefficient defined by medium viscosity and associated Reynold's number) drag_coefficient*cross-section*substrate_density*c^2 as per http://arxiv.org/abs/1503.07675 equation S2. The stars inertially blow on through a viscous medium while the DM is held up a little more in the viscous medium and gas much more in the viscous medium. A Pioneer 10 and 11 cross_section value 0.24 cm^2/g may be computed from the NASA published Pioneer dimensions (pi/4)*pioneer_diameter^2/pioneer_mass = (pi/4)*274^2/241,000 = 0.24 cm^2/g and Pioneer 10 and 11 deceleration can be considered substantiation of http://arxiv.org/abs/1503.07675 DM separation mechanism. What is the viscous medium? There has been theoretical work on vacuum viscosity arXiv:0806.3165v3 [hep-th] 14 Nov 2008 Hydrodynamics of spacetime and vacuum viscosity that may be applicable here. Richard D Saam |
#10
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Can dark matter be small objects?
[[Mod. note -- I'm allowing this last posting, but in the absence of
*new* points I think it's time to close this thread. -- jt]] On 4/25/15 9:05 PM, Richard D. Saam wrote: [[Mod. note -- Note that arXiv:1503.07675 does NOT claim to have detected a nonzero self-interaction cross section of dark matter. Rather, it claims to have place an *upper limit* on any such cross section. -- jt]] Yes, your observation as well as Steve Willner's previous is correct and my deficiency. Amplification is necessary. This reference http://arxiv.org/abs/1503.07675 indicates dark matter cross-section and resultant drag characteristics for 72 studied galactic collisions 0.47 cm^2/g This places limits on the DM object size(D) and DM object density(rho_DM_object) of dark matter objects assuming spherical DM objects with area(A) cross-section = (pi/4)*D^2 and DM object volume(V) = (pi/6)*D^3 and DM object density(rho) = M/V then 0.47 cm^2/g = (A/M)*(V/V) = (V/M)*(A/V) = (1/rho)*((pi/4)*D^2/((pi/6)*D^3)) = (1/rho)*(3/2)/D therefore D = ((3/2)/0.47)/rho cm N = rho_DM/M M = rho_DM_object*V DM Mean Free Path = 1/(sqrt(2)*pi*N*D^2) assume DM aggregate density(rho_DM) = 1x10^-24 g/cm^3 then for the limiting DM cross_section .47 cm^2/g DM object density(rho) DM object size(D) DM Mean Free Path g/cm^3 cm kpc 0.0319 99.8 122 0.319 9.98 122 3.19 .998 122 (any DM cross-section larger than 0.47 cm^2/g with DM Mean Free Path 122 kpc 'close to the size of these colliding galaxies' would be seen optically) A Pioneer 10 and 11 cross_section value 0.24 cm^2/g may be computed from the NASA published Pioneer dimensions (pi/4)*pioneer_diameter^2/pioneer_mass = (pi/4)*274^2/241,000 = 0.24 cm^2/g then for the Pioneer cross_section .24 cm^2/g DM object density(rho) DM object size(D) DM Mean Free Path g/cm^3 cm kpc 0.313 20.0 238 0.625 9.98 238 0.0625 99.8 238 0.0228 Pioneer as sphere 274 Pioneer size 238 (any DM cross-section ~ Pioneer 0.24 cm^2/g with DM Mean Free Path 238 kpc would not be seen optically) then for the cross_section .01 cm^2/g (0.47 cm^2/g) DM object density(rho) DM object size(D) DM Mean Free Path g/cm^3 cm kpc 1.5 99.8 5,720 0.15 998 5,720 0.015 9,980 5,720 (any DM cross-section ~ 0.01 cm^2/g with DM Mean Free Path 5,720 kpc would not be seen optically) then for the cross_section .001 cm^2/g (0.47 cm^2/g) DM object density(rho) DM object size(D) DM Mean Free Path g/cm^3 cm kpc 1.5 998 57,300 0.15 9,980 57,300 0.015 99,800 57,300 (any DM cross-section ~ 0.001 cm^2/g with DM Mean Free Path 57,300 kpc would not be seen optically) These calculations can be viewed in the context of the red, blue and green dots in http://arxiv.org/abs/1503.07675 Figure 1, the represented entities could be interpreted as being separated in accordance with cross-section gas 5E7 cm^2/g (calculated atom area/mass) dark matter 0.47 cm^2/g stars 7E-12 cm^2/g (calculated sun area/mass) with the hydrodynamic mechanism (with a drag coefficient defined by medium viscosity and associated Reynold's number) drag_coefficient*cross-section*substrate_density*c^2 as per http://arxiv.org/abs/1503.07675 equation S2. The stars inertially blow on through a viscous medium while the DM is held up a little more in the viscous medium and gas much more in the viscous medium. and Pioneer 10 and 11 deceleration can be considered substantiation of http://arxiv.org/abs/1503.07675 DM separation mechanism. The Bullet Cluster provides further evidence of DM decceleration analogous to Pioneer deceleration http://arxiv.org/abs/astro-ph/0608408 http://en.wikipedia.org/wiki/Bullet_Cluster Bullet Cluster E0657-56 length 7.714E+23 cm 250 kpc Bullet Cluster E0657-56 time after collision 4.730E+15 sec 1.50E+08 years Bullet Cluster E0657-56 acceleration 2*length/time^2 = 6.895E-08 cm/sec^2 This deceleration is of the same order as the Pioneer deceleration. What is the viscous medium? There has been theoretical work on vacuum viscosity arXiv:0806.3165v3 [hep-th] 14 Nov 2008 Hydrodynamics of spacetime and vacuum viscosity that may be applicable here. The DM has to be very cold so as not to observed. DM object thermal emissivity may be an indicator of these low temperatures. Associated extremely long wavelengths are not measurable at this time as calculated by established black body spectrum peak wave length theory. wave length (cm) = h*c/(4.96536456*Boltzmann*T) Emission T K Emission wave length (cm) 2.2E+01 1.3E-02 2.7E+00 1.1E-01 1.0E+00 2.9E-01 1.0E-01 2.9E+00 1.0E-02 2.9E+01 1.0E-03 2.9E+02 1.0E-04 2.9E+03 1.0E-05 2.9E+04 1.0E-06 2.9E+05 1.0E-07 2.9E+06 1.0E-08 2.9E+07 1.0E-09 2.9E+08 1.0E-10 2.9E+09 1.0E-11 2.9E+10 1.0E-12 2.9E+11 1.0E-13 2.9E+12 1.0E-14 2.9E+13 1.0E-15 2.9E+14 1.0E-16 2.9E+15 1.0E-17 2.9E+16 So the secondary (solid, liquid or other) phase DM could be there and at a temperature CMBR 2.7K and produced as a BBN (solid, liquid or other) phase separate from gaseous H, He Li and not in thermal equilibrium with BBN produced and measured universe gaseous H, He Li? and currently not thermally measurable or as a baryonic acoustic oscillation at first light (380,000 yrs) Hydrogen molecular bonding mechanisms at these extremely cold temperatures would provide a stable DM object. Richard D Saam |
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