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Self-Interacting Dark Matter
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wlandsman
Jul 4, 2015, 4:44:03 PM7/4/15
to
We have no confirmed non-gravitational detection of dark matter
either astrophysically or in the laboratory. But that does not
mean that we cannot learn anything about dark matter. Recently,
Massey et al. a claimed possible detection of dark matter interacting
with itself in a galaxy in the cluster Abell 3827.
http://arstechnica.com/science/2015/04/new-evidence-that-dark-matter-could-be-self-interacting/
http://www.eso.org/public/usa/news/eso1514/
The authors use gravitational lensing to map out the dark matter
distribution in the galaxy cluster. They highlight a galaxy falling
into the (dark matter) cluster core, in which the dark matter halo
of the galaxy appears to lag behind its visible contents. They
argue that the dark matter halo is slowed down by its interaction
with the dark matter cluster core (whereas the baryonic contents
experience no interaction)
I have two questions about this work.
1. How likely is it that this tentative detection will be confirmed
(or disproved)?
2. How much does a measurement of self-interaction actually tell
us about dark matter.
For the first question, I am astonished by the rapid progress in
the use of gravitational lensing to map out the distribution of
non-baryonic dark matter. (I was previously impressed with the
rapid progress in microlensing to rule out significant baryonic
dark matter.) But Massey et al. point out the fortuitous circumstances
that made their observation possible. In particular they require
a nearby cluster (so that small lag can be measured) and a complex
background galaxy (so the the mass distribution of the lensing
galaxy can be measured). I should think we need measurements
of three or four such systems giving consistent results before we
can fully believe we have detected self-interacting dark matter.
As for what this measurement can tell us about dark matter, the
fact that we *don't* see self-interaction at the galaxy cluster
level (e.g. the bullet cluster) but do see at the galaxy level
suggests that it might solve one of the very few problems with
Lambda CDM. Lambda CDM works extremely well with large-scale
structure but less well at the galaxy level, perhaps because because
current models neglect dark matter self-interaction.
But the Massey et al measurements only return a single interesting
parameter-- the self-interaction rate -- that doesn't satisfy the
question of what dark matter is. In the July 2015 issue of
Scientific American (quarantined) Dobrescu and Lincoln suggest
that there are a variety of dark matter particles and "dark forces"
analogous to electromagnetism which mediate only between dark
particles. If true, then we may have a new tool for studying
dark matter but it is an extremely crude one at best.
--Wayne
either astrophysically or in the laboratory. But that does not
mean that we cannot learn anything about dark matter. Recently,
Massey et al. a claimed possible detection of dark matter interacting
with itself in a galaxy in the cluster Abell 3827.
http://arstechnica.com/science/2015/04/new-evidence-that-dark-matter-could-be-self-interacting/
http://www.eso.org/public/usa/news/eso1514/
The authors use gravitational lensing to map out the dark matter
distribution in the galaxy cluster. They highlight a galaxy falling
into the (dark matter) cluster core, in which the dark matter halo
of the galaxy appears to lag behind its visible contents. They
argue that the dark matter halo is slowed down by its interaction
with the dark matter cluster core (whereas the baryonic contents
experience no interaction)
I have two questions about this work.
1. How likely is it that this tentative detection will be confirmed
(or disproved)?
2. How much does a measurement of self-interaction actually tell
us about dark matter.
For the first question, I am astonished by the rapid progress in
the use of gravitational lensing to map out the distribution of
non-baryonic dark matter. (I was previously impressed with the
rapid progress in microlensing to rule out significant baryonic
dark matter.) But Massey et al. point out the fortuitous circumstances
that made their observation possible. In particular they require
a nearby cluster (so that small lag can be measured) and a complex
background galaxy (so the the mass distribution of the lensing
galaxy can be measured). I should think we need measurements
of three or four such systems giving consistent results before we
can fully believe we have detected self-interacting dark matter.
As for what this measurement can tell us about dark matter, the
fact that we *don't* see self-interaction at the galaxy cluster
level (e.g. the bullet cluster) but do see at the galaxy level
suggests that it might solve one of the very few problems with
Lambda CDM. Lambda CDM works extremely well with large-scale
structure but less well at the galaxy level, perhaps because because
current models neglect dark matter self-interaction.
But the Massey et al measurements only return a single interesting
parameter-- the self-interaction rate -- that doesn't satisfy the
question of what dark matter is. In the July 2015 issue of
Scientific American (quarantined) Dobrescu and Lincoln suggest
that there are a variety of dark matter particles and "dark forces"
analogous to electromagnetism which mediate only between dark
particles. If true, then we may have a new tool for studying
dark matter but it is an extremely crude one at best.
--Wayne
Phillip Helbig (undress to reply)
Jul 5, 2015, 1:15:53 PM7/5/15
to
In article <690be869-8547-48b7...@googlegroups.com>,
tentative detection.
> 2. How much does a measurement of self-interaction actually tell
> us about dark matter.
We don't know what dark matter is. Some ideas for it are
self-interacting, others are not.
> For the first question, I am astonished by the rapid progress in
> the use of gravitational lensing to map out the distribution of
> non-baryonic dark matter. (I was previously impressed with the
> rapid progress in microlensing to rule out significant baryonic
> dark matter.) But Massey et al. point out the fortuitous circumstances
> that made their observation possible. In particular they require
> a nearby cluster (so that small lag can be measured) and a complex
> background galaxy (so the the mass distribution of the lensing
> galaxy can be measured). I should think we need measurements
> of three or four such systems giving consistent results before we
> can fully believe we have detected self-interacting dark matter.
Yes, they should definitely be confirmed. As you note, it needs a
rather unlikely system, but now with big telescopes surveying the whole
sky on a regular basis (or, if not now, soon), even unlikely systems can
be found.
> As for what this measurement can tell us about dark matter, the
> fact that we *don't* see self-interaction at the galaxy cluster
> level (e.g. the bullet cluster) but do see at the galaxy level
> suggests that it might solve one of the very few problems with
> Lambda CDM. Lambda CDM works extremely well with large-scale
> structure but less well at the galaxy level, perhaps because because
> current models neglect dark matter self-interaction.
Perhaps. This would be a refinement to an existing idea, which is the
way science almost always progresses.
> But the Massey et al measurements only return a single interesting
> parameter-- the self-interaction rate -- that doesn't satisfy the
> question of what dark matter is.
Sure, but one can't expect more.
> In the July 2015 issue of
> Scientific American (quarantined) Dobrescu and Lincoln suggest
> that there are a variety of dark matter particles and "dark forces"
> analogous to electromagnetism which mediate only between dark
> particles.
Could be. It would be strange if the only unknown matter which exists
is that for which we now have evidence.
wlandsman <wlan...@gmail.com> writes:
> I have two questions about this work.
> 1. How likely is it that this tentative detection will be confirmed
> (or disproved)?
Pretty much impossible to say. As you note, it is a new result, a
> I have two questions about this work.
> 1. How likely is it that this tentative detection will be confirmed
> (or disproved)?
tentative detection.
> 2. How much does a measurement of self-interaction actually tell
> us about dark matter.
self-interacting, others are not.
> For the first question, I am astonished by the rapid progress in
> the use of gravitational lensing to map out the distribution of
> non-baryonic dark matter. (I was previously impressed with the
> rapid progress in microlensing to rule out significant baryonic
> dark matter.) But Massey et al. point out the fortuitous circumstances
> that made their observation possible. In particular they require
> a nearby cluster (so that small lag can be measured) and a complex
> background galaxy (so the the mass distribution of the lensing
> galaxy can be measured). I should think we need measurements
> of three or four such systems giving consistent results before we
> can fully believe we have detected self-interacting dark matter.
rather unlikely system, but now with big telescopes surveying the whole
sky on a regular basis (or, if not now, soon), even unlikely systems can
be found.
> As for what this measurement can tell us about dark matter, the
> fact that we *don't* see self-interaction at the galaxy cluster
> level (e.g. the bullet cluster) but do see at the galaxy level
> suggests that it might solve one of the very few problems with
> Lambda CDM. Lambda CDM works extremely well with large-scale
> structure but less well at the galaxy level, perhaps because because
> current models neglect dark matter self-interaction.
way science almost always progresses.
> But the Massey et al measurements only return a single interesting
> parameter-- the self-interaction rate -- that doesn't satisfy the
> question of what dark matter is.
> In the July 2015 issue of
> Scientific American (quarantined) Dobrescu and Lincoln suggest
> that there are a variety of dark matter particles and "dark forces"
> analogous to electromagnetism which mediate only between dark
> particles.
is that for which we now have evidence.
Richard D. Saam
Jul 6, 2015, 10:58:01 PM7/6/15
to
On 7/4/15 3:44 PM, wlandsman wrote:
> We have no confirmed non-gravitational detection of dark matter
> either astrophysically or in the laboratory. But that does not
> mean that we cannot learn anything about dark matter. Recently,
> Massey et al. a claimed possible detection of dark matter interacting
> with itself in a galaxy in the cluster Abell 3827.
>
> 1. http://arstechnica.com/science/2015/04/new-evidence-that-dark-matter-could-be-self-interacting/
> We have no confirmed non-gravitational detection of dark matter
> either astrophysically or in the laboratory. But that does not
> mean that we cannot learn anything about dark matter. Recently,
> Massey et al. a claimed possible detection of dark matter interacting
> with itself in a galaxy in the cluster Abell 3827.
>
> 2. http://www.eso.org/public/usa/news/eso1514/
3. http://arxiv.org/abs/1504.06576
4. http://arxiv.org/abs/1503.07675
The ref 3 complements Massey et al. work ref 1,2
"Further studies of such systems are imperative to establish
if the indication from A3827 for a non-zero self-interaction
cross section (of order 1 cm^2/g) is indeed correct."
"It should therefore be clear that A3827 is no
more sensitive to DM self-interactions than other systems
considered in this context and can certainly not be used to
probe cross-sections as small as 10^(-4) cm^2 g^(-1)"
This conclusion from ref 3
would indicated that the <0.47 cm^2/g cross-section ref 4
may be weighted more towards .47 cm^2/g
Ref 1 indicates "it 'on the order 1 cm^2/g'
would be just right to solve the observational issues with the leading
dark matter model, which calls for a cross-section between 0.1 and one
square centimeter per gram
My question- What is the leading dark matter model that predicts DM
cross-section on the order of 1 cm^2/g ?
>
> The authors use gravitational lensing to map out the dark matter
> distribution in the galaxy cluster. They highlight a galaxy falling
> into the (dark matter) cluster core, in which the dark matter halo
> of the galaxy appears to lag behind its visible contents. They
> argue that the dark matter halo is slowed down by its interaction
> with the dark matter cluster core (whereas the baryonic contents
> experience no interaction)
Dark matter slowing down at a rate other than observed baryonic contents
> The authors use gravitational lensing to map out the dark matter
> distribution in the galaxy cluster. They highlight a galaxy falling
> into the (dark matter) cluster core, in which the dark matter halo
> of the galaxy appears to lag behind its visible contents. They
> argue that the dark matter halo is slowed down by its interaction
> with the dark matter cluster core (whereas the baryonic contents
> experience no interaction)
does not in itself exclude a baryonic DM character.
Give this evidence alone,
DM could be a different baryonic size/mass distribution
providing a different lag character.
>
> I have two questions about this work.
> 1. How likely is it that this tentative detection will be confirmed
> (or disproved)?
see ref 4 "Chandra and Hubble Space Telescopes we have now observed 72
> I have two questions about this work.
> 1. How likely is it that this tentative detection will be confirmed
> (or disproved)?
collisions, including both `major' and `minor' mergers"
for concluded aggregate <0.47 cm^2/g cross-section
> 2. How much does a measurement of self-interaction actually tell
> us about dark matter.
Ref1 provides the DM lag mechanism "The more they collide (or the higher
> us about dark matter.
the cross-section), the more a blob of dark matter should lag, due to
the friction created by the colliding particles"
Another mechanism may be DM drag or lag
due to vacuum (momentum transfer) viscosity
Vacuum viscosity is physically discussed in
arXiv:0806.3165v3 [hep-th] 14 Nov 2008
Hydrodynamics of spacetime and vacuum viscosity
>
> For the first question, I am astonished by the rapid progress in
> the use of gravitational lensing to map out the distribution of
> non-baryonic dark matter. (I was previously impressed with the
> rapid progress in microlensing to rule out significant baryonic
> dark matter.) But Massey et al. point out the fortuitous circumstances
> that made their observation possible. In particular they require
> a nearby cluster (so that small lag can be measured) and a complex
> background galaxy (so the the mass distribution of the lensing
> galaxy can be measured). I should think we need measurements
> of three or four such systems giving consistent results before we
> can fully believe we have detected self-interacting dark matter.
>
see ref 4 for Chandra and Hubble Space Telescopes we have now observed
> For the first question, I am astonished by the rapid progress in
> the use of gravitational lensing to map out the distribution of
> non-baryonic dark matter. (I was previously impressed with the
> rapid progress in microlensing to rule out significant baryonic
> dark matter.) But Massey et al. point out the fortuitous circumstances
> that made their observation possible. In particular they require
> a nearby cluster (so that small lag can be measured) and a complex
> background galaxy (so the the mass distribution of the lensing
> galaxy can be measured). I should think we need measurements
> of three or four such systems giving consistent results before we
> can fully believe we have detected self-interacting dark matter.
>
72 collisions, including both `major' and `minor' mergers
> As for what this measurement can tell us about dark matter, the
> fact that we *don't* see self-interaction at the galaxy cluster
> level (e.g. the bullet cluster)
Ref 1:"In the Bullet Cluster observations, no lag was found, but the
> fact that we *don't* see self-interaction at the galaxy cluster
> level (e.g. the bullet cluster)
study was not precise enough to rule it out entirely.
But the study did constrain it;
if dark matter self-interactions were taking place,
they weren't doing so that often
(the cross-section had to be 1.25 square centimeters per gram or less)."
Also pointing to other work
The Bullet Cluster provides further evidence of DM decceleration
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 = 6.9E-08 cm/sec^2
This deceleration is of the same order
as the Pioneer deceleration.
A Pioneer 10 and 11 cross_section value 0.24 cm^2/g
(within range of Ref 1,3,4)
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
with universe critical density (3/8pi)*H^2/G ~ 1x10^-29 g/cm^3
6.9E-08 = Cd * .24 * 1x10^-29 * c^2 = 2x10^-9 cm/sec^2
where a reasonable unitless hydrodynamic drag coefficient Cd = 32
The case for Pioneers' deceleration
predominately due to thermal affects
http://arxiv.org/pdf/1204.2507v1
may have been premature
considering reported decelerations
did not include the residual constant values
as these spacecraft entered intergalactic space
with concurrent diminishing thermal affects.
https://groups.google.com/forum/#!searchin/sci.astro.research/wimps/sci.astro.research/5vpM6FvQQ-E/FJy5LOLrSOEJ
Further data analysis is required
particularly with Pioneers' spin deceleration
as a vacuum viscosity (momentum transfer) probe
that was entirely excluded from
http://arxiv.org/pdf/1204.2507v1.
> but do see at the galaxy level
> suggests that it might solve one of the very few problems with
> Lambda CDM. Lambda CDM works extremely well with large-scale
> structure but less well at the galaxy level, perhaps because because
> current models neglect dark matter self-interaction.
arXiv:0806.3165v3 [hep-th] 14 Nov 2008
Hydrodynamics of spacetime and vacuum viscosity
Lambda CDM appears to be too smooth & too perfect
> But the Massey et al measurements only return a single interesting
> parameter-- the self-interaction rate -- that doesn't satisfy the
> question of what dark matter is. In the July 2015 issue of
> Scientific American (quarantined) Dobrescu and Lincoln suggest
> that there are a variety of dark matter particles and "dark forces"
> analogous to electromagnetism which mediate only between dark
> particles.
Seems too complicated.
> parameter-- the self-interaction rate -- that doesn't satisfy the
> question of what dark matter is. In the July 2015 issue of
> Scientific American (quarantined) Dobrescu and Lincoln suggest
> that there are a variety of dark matter particles and "dark forces"
> analogous to electromagnetism which mediate only between dark
> particles.
> If true, then we may have a new tool for studying
> dark matter but it is an extremely crude one at best.
Given the logarithmic nature of the universe,
> dark matter but it is an extremely crude one at best.
having a value within one order of magnitude should be very useful.
Richard D Saam for comments
>
> --Wayne
>
Jos Bergervoet
Jul 9, 2015, 1:10:13 AM7/9/15
to
On 7/5/2015 7:15 PM, Phillip Helbig (undress to reply) wrote:
> In article <690be869-8547-48b7...@googlegroups.com>, wlandsman <wlan...@gmail.com> writes:
...
> In article <690be869-8547-48b7...@googlegroups.com>, wlandsman <wlan...@gmail.com> writes:
>> In the July 2015 issue of
>> Scientific American (quarantined) Dobrescu and Lincoln suggest
>> that there are a variety of dark matter particles and "dark forces"
>> analogous to electromagnetism which mediate only between dark
>> particles.
>
> Could be. It would be strange if the only unknown matter which exists
> is that for which we now have evidence.
Perhaps not. Seen from the standard model of particle physics
>> Scientific American (quarantined) Dobrescu and Lincoln suggest
>> that there are a variety of dark matter particles and "dark forces"
>> analogous to electromagnetism which mediate only between dark
>> particles.
>
> Could be. It would be strange if the only unknown matter which exists
> is that for which we now have evidence.
it could mean (for instance) that the only unknown particle to
be added is the axion.
That would just mean that the standard model of particle physics
is basically correct (i.e. that it is complete at ordinary
energy levels, while of course some additions might still be
found if you go way up to the Planck scale.
So, would it be "strange" if we only need the axion to complete
our working set of particles?
--
Jos
Phillip Helbig (undress to reply)
Jul 9, 2015, 1:11:19 AM7/9/15
to
In article <U4CdnVHgMqQGdgTI...@giganews.com>, "Richard D.
bricks. Or back issues of the ApJ. But other arguments do. Ditto for
a significant fraction of dark matter being baryonic.
> Give this evidence alone,
> DM could be a different baryonic size/mass distribution
> providing a different lag character.
Sure, but "this evidence alone" is not a good choice when there is other
evidence available.
Saam" <rds...@att.net> writes:
> Dark matter slowing down at a rate other than observed baryonic contents
> does not in itself exclude a baryonic DM character.
True. Optical depth alone does not exclude that dark matter is made of
> Dark matter slowing down at a rate other than observed baryonic contents
> does not in itself exclude a baryonic DM character.
bricks. Or back issues of the ApJ. But other arguments do. Ditto for
a significant fraction of dark matter being baryonic.
> Give this evidence alone,
> DM could be a different baryonic size/mass distribution
> providing a different lag character.
evidence available.
Richard D. Saam
Jul 11, 2015, 2:47:31 PM7/11/15
to
1. Transparency as per above optical depth concept
does not rule out small bricks composing galactic halos
in aggregate ~1x10-24 g/cm^3.
2. Calculation of nucleosynthetic H, He abundances correlate with
observed values based on their gaseous EM absorptivity and emissions,
but all H, He may not be in the gaseous state.
Present nucleosynthetic calculations do not take into account plasma
colligative properties such as may be observed
by high atomic Z (gold) work performed
at RHIC Brookhaven National Laboratory
influencing H nucleosynthetic phase magnitude relationships.
3. DM Bricks not heating up due to CMBR over the billions of years
appears to rule out their baryonic character,
but DM bricks may be in thermal equilibrium
with another much colder phase
associated with universe density
presently at ~1x10-29 g/cm^3 ~H^2/G
rather than CMBR(at ~1x10-34 g/cm^3)
rendering the DM bricks electromagnetically unobserved.
4.CMBR fluctuations characterizing DM
and observed ~4% universe baryonic matter correlated to BAO
are limited due to
finite CMBR Black Body WMAP and Planck observation
at circa 160 GHz of universe with near infinitely available EM spectra .
5. Previous discussion on this newsgroup (jacob et al) reference early
galactic formation that may be fueled by DM baryonic mass action.
Logical conclusion:
DM bricks could be extremely cold nucleosynthetic hydrogen.
How cold?
Probably ~1x10^-15 K
Richard D. Saam
[[Mod. note -- It seems unlikely to me that such "bricks" would survive
for many Gigayears at a temperature far BELOW that of the CMBR. -- jt]]
Phillip Helbig (undress to reply)
Jul 13, 2015, 3:22:06 PM7/13/15
to
In article <MtidnVogTcvBkwLI...@giganews.com>, "Richard D.
gives us good upper limits on the amount of baryons.
> 2. Calculation of nucleosynthetic H, He abundances correlate with
> observed values based on their gaseous EM absorptivity and emissions,
> but all H, He may not be in the gaseous state.
> Present nucleosynthetic calculations do not take into account plasma
> colligative properties such as may be observed
> by high atomic Z (gold) work performed
> at RHIC Brookhaven National Laboratory
> influencing H nucleosynthetic phase magnitude relationships.
Is there any evidence that either of these could increase the allowed
number of baryons by a factor of 10?
> 3. DM Bricks not heating up due to CMBR over the billions of years
> appears to rule out their baryonic character,
> but DM bricks may be in thermal equilibrium
> with another much colder phase
> associated with universe density
> presently at ~1x10-29 g/cm^3 ~H^2/G
> rather than CMBR(at ~1x10-34 g/cm^3)
> rendering the DM bricks electromagnetically unobserved.
By definition, DM does not interact electromagnetically. It does
interact gravitationally. Assuming DM bricks, as opposed to baryonic
bricks (which is what I originally meant), then there must be
self-interaction. In that case, however, it is unclear why there are
not DM planets etc, which could be seen via microlensing.
> 4.CMBR fluctuations characterizing DM
> and observed ~4% universe baryonic matter correlated to BAO
> are limited due to
> finite CMBR Black Body WMAP and Planck observation
> at circa 160 GHz of universe with near infinitely available EM spectra .
First, explain why this "limitation" affects the conclusions. Second,
you are just as limited with respect to your alternative theory.
> Logical conclusion:
> DM bricks could be extremely cold nucleosynthetic hydrogen.
> How cold?
> Probably ~1x10^-15 K
Saam" <rds...@att.net> writes:
> 1. Transparency as per above optical depth concept
> does not rule out small bricks composing galactic halos
> in aggregate ~1x10-24 g/cm^3.
Assuming that they are baryonic, then they are ruled out because BBN
> 1. Transparency as per above optical depth concept
> does not rule out small bricks composing galactic halos
> in aggregate ~1x10-24 g/cm^3.
gives us good upper limits on the amount of baryons.
> 2. Calculation of nucleosynthetic H, He abundances correlate with
> observed values based on their gaseous EM absorptivity and emissions,
> but all H, He may not be in the gaseous state.
> Present nucleosynthetic calculations do not take into account plasma
> colligative properties such as may be observed
> by high atomic Z (gold) work performed
> at RHIC Brookhaven National Laboratory
> influencing H nucleosynthetic phase magnitude relationships.
number of baryons by a factor of 10?
> 3. DM Bricks not heating up due to CMBR over the billions of years
> appears to rule out their baryonic character,
> but DM bricks may be in thermal equilibrium
> with another much colder phase
> associated with universe density
> presently at ~1x10-29 g/cm^3 ~H^2/G
> rather than CMBR(at ~1x10-34 g/cm^3)
> rendering the DM bricks electromagnetically unobserved.
interact gravitationally. Assuming DM bricks, as opposed to baryonic
bricks (which is what I originally meant), then there must be
self-interaction. In that case, however, it is unclear why there are
not DM planets etc, which could be seen via microlensing.
> 4.CMBR fluctuations characterizing DM
> and observed ~4% universe baryonic matter correlated to BAO
> are limited due to
> finite CMBR Black Body WMAP and Planck observation
> at circa 160 GHz of universe with near infinitely available EM spectra .
you are just as limited with respect to your alternative theory.
> Logical conclusion:
> DM bricks could be extremely cold nucleosynthetic hydrogen.
> How cold?
> Probably ~1x10^-15 K
> [[Mod. note -- It seems unlikely to me that such "bricks" would survive
> for many Gigayears at a temperature far BELOW that of the CMBR. -- jt]]
Right.
> for many Gigayears at a temperature far BELOW that of the CMBR. -- jt]]
David Staup
Jul 14, 2015, 4:42:33 AM7/14/15
to
On 7/13/2015 2:22 PM, Phillip Helbig (undress to reply) wrote:
>> [[Mod. note -- It seems unlikely to me that such "bricks" would survive
>> >for many Gigayears at a temperature far BELOW that of the CMBR. -- jt]]
> Right.
If these bricks do not interact electromagnetically then there is no way
>> [[Mod. note -- It seems unlikely to me that such "bricks" would survive
>> >for many Gigayears at a temperature far BELOW that of the CMBR. -- jt]]
> Right.
the CMBR could affect their temperature, is there?
Jos Bergervoet
Jul 15, 2015, 9:38:36 PM7/15/15
to
On 7/13/2015 9:22 PM, Phillip Helbig (undress to reply) wrote:
..
If DM consists of axions, they still have some interaction
with the EM field, although more complicated than other
particles (they are not a direct source term).
< http://depts.washington.edu/admx/home.html >
Or if DM consists of neutrinos, those can still have an
anapole moment, which leaves some EM interaction, although
again weaker than ordinary dipole or monopole interactions.
> It does interact gravitationally.
I think "It does interact predominantly gravitationally
on large scales" is covering the situation better. That
would not rule out interactions of any other kind and
even allow for them to become significant in dense
regions on (sub-)galactic scales.
> Assuming DM bricks, as opposed to baryonic
> bricks (which is what I originally meant), then there must be
> self-interaction. In that case, however, it is unclear why there are
> not DM planets etc, which could be seen via microlensing.
The "other interactions" might be such that those planets
remain much smaller than usual planet sizes (instead they
might not grow larger than the size of, well, bricks!)
But of course then they wouldn't fit the definition of
planet. At least that definition is made very rigorous. :^)
>> [[Mod. note -- It seems unlikely to me that such "bricks" would survive
>> for many Gigayears at a temperature far BELOW that of the CMBR. -- jt]]
>
> Right.
Agreed (but it's only likelihood guessing!)
--
Jos
..
> By definition, DM does not interact electromagnetically.
I think you take the definition too rigorously.
If DM consists of axions, they still have some interaction
with the EM field, although more complicated than other
particles (they are not a direct source term).
< http://depts.washington.edu/admx/home.html >
Or if DM consists of neutrinos, those can still have an
anapole moment, which leaves some EM interaction, although
again weaker than ordinary dipole or monopole interactions.
> It does interact gravitationally.
I think "It does interact predominantly gravitationally
on large scales" is covering the situation better. That
would not rule out interactions of any other kind and
even allow for them to become significant in dense
regions on (sub-)galactic scales.
> Assuming DM bricks, as opposed to baryonic
> bricks (which is what I originally meant), then there must be
> self-interaction. In that case, however, it is unclear why there are
> not DM planets etc, which could be seen via microlensing.
remain much smaller than usual planet sizes (instead they
might not grow larger than the size of, well, bricks!)
But of course then they wouldn't fit the definition of
planet. At least that definition is made very rigorous. :^)
>> [[Mod. note -- It seems unlikely to me that such "bricks" would survive
>> for many Gigayears at a temperature far BELOW that of the CMBR. -- jt]]
>
> Right.
--
Jos
Phillip Helbig (undress to reply)
Jul 15, 2015, 9:39:52 PM7/15/15
to
In article <mo1mql$pib$1...@dont-email.me>, David Staup
The claim was:
3. DM Bricks not heating up due to CMBR over the billions of years
appears to rule out their baryonic character,
but DM bricks may be in thermal equilibrium
with another much colder phase
associated with universe density
presently at ~1x10-29 g/cm^3 ~H^2/G
rather than CMBR(at ~1x10-34 g/cm^3)
rendering the DM bricks electromagnetically unobserved.
So talking about baryonic, and hence electromagnetically interacting,
matter, but with another "explanation" for the cold temperature, which
to me seems a bit speculative and ad-hoc.
3. DM Bricks not heating up due to CMBR over the billions of years
appears to rule out their baryonic character,
but DM bricks may be in thermal equilibrium
with another much colder phase
associated with universe density
presently at ~1x10-29 g/cm^3 ~H^2/G
rather than CMBR(at ~1x10-34 g/cm^3)
rendering the DM bricks electromagnetically unobserved.
matter, but with another "explanation" for the cold temperature, which
to me seems a bit speculative and ad-hoc.
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