Does dark matter contribute to the mass of planets and stars?

[johndevers@iprimus.com.au]

If dark matter can't even escape the surface of the earth then why
don't scientists include dark matter into their models and
calculations of the mass of planets and stars?

Over billions of years wouldn't trillions of tons of dark matter fall
on planets and stars?

As dark matter only interacts gravitationally wouldn't it accumulate
in a superposition with baryonic matter and orbit around inside the
Earth?

How much of Earth or the Sun is made up of dark matter?

If I recall correctly dark matter makes up about 23% of the mass of
the universe and would have an overall density equal to about 1
hydrogen atom per cc whereas our solar system has on average a
baryonic matter density of about 9 hydrogen atoms per cc.

Would this non interactive extra mass accumulating on large enough
planets and stars matter when modeling fusion and fission rates in
stars? or proton neutron ratios and the makeup of neutron stars?

The speed of dark matter is about 6 miles per second (9km/s) Ref 1.

Neutron stars have an escape velocity of around 150,000 km/s Ref 2.

The sun has an escape velocity of around 600 km/sec. Ref 3.

Jupiter has an escape velocity of 59.5 km/s

Earth has an escape velocity of 11.2 km/s

Ref 1

http://www.space.com/scienceastronomy/060221_stues_dark_matter.html

Ref 2

http://en.wikipedia.org/wiki/Neutron_star

Ref 3
www.ips.gov.au/Educational/2/1/4

[mathman]

If dark matter can't even escape the surface of the earth

Your assertion is incorrect. Dark matter passes through the earth as if it wasn't there. Experiments to detect dark matter are very difficult because of this.

[Ian Parker]

On 27 Jul, 19:51, johndev...@iprimus.com.au wrote:
> If dark matter can't even escape the surface of the earth then why
> don't scientists include dark matter into their models and
> calculations of the mass of planets and stars?
>
> Over billions of years wouldn't trillions of tons of dark matter fall
> on planets and stars?
>
> As dark matter only interacts gravitationally wouldn't it accumulate
> in a superposition with baryonic matter and orbit around inside the
> Earth?
>
> How much of Earth or the Sun is made up of dark matter?
>
> If I recall correctly dark matter makes up about 23% of the mass of
> the universe and would have an overall density equal to about 1
> hydrogen atom per cc whereas our solar system has on average a
> baryonic matter density of about 9 hydrogen atoms per cc.
>
> Would this non interactive extra mass accumulating on large enough
> planets and stars matter when modeling fusion and fission rates in
> stars? =A0or proton neutron ratios and the makeup of neutron stars?
>
> The speed of dark matter is about 6 miles per second (9km/s) Ref 1.
>
> Neutron stars have an escape velocity of around 150,000 km/s =A0Ref 2.
>
> The sun has an escape velocity of around 600 km/sec. Ref 3.
>
> Jupiter has an escape velocity of 59.5 km/s
>
> Earth has an escape velocity of 11.2 km/s
>
> Ref 1
>
> http://www.space.com/scienceastronomy/060221_stues_dark_matter.html
>
> Ref 2
>
> http://en.wikipedia.org/wiki/Neutron_star
>
> Ref 3www.ips.gov.au/Educational/2/1/4

I would say very little. Let us however give a more scientific answer
and see how we could test this. If an appeciable fraction of the Earth/
Sun is dark matter the Earth will be surrounded by a clould. This
means that there is not an accurate inverse square law. Accurate
orbital measurements show no trace of such an effect.

There has been a Pioneer anomaly which could be due to Dark Matter.
There are however other explanations based on the geometry of the
spacecraft. "New Horizon" will act as a check on this. We should be
cautious.

The Earth cannot capture DM for one very simple reason. DM lands on
Earth at 11.2km/s + and comes out the other side at the same speed.

- Ian Parker

[p.brane@by.co.uk]

In article <00dd54c0-a0a9-4f7e-81d5-
f9d692bf3f7d@x35g2000hsb.googlegroups.com>, ianparker2@gmail.com says...
> The Earth cannot capture DM for one very simple reason. DM lands on
> Earth at 11.2km/s + and comes out the other side at the same speed.
>
> - Ian Parker
>

If it was matter presumably it has mass? (isn't that the point?)
A mass passing through the earth at "11.2 km/s +" would leave what size
hole?

Do I need to go out and buy a hat?

-peter-

[mathman]

If it was matter presumably it has mass? (isn't that the point?)
A mass passing through the earth at "11.2 km/s +" would leave what size
hole?

Do I need to go out and buy a hat?

-peter-

The mass and size, although unknown, are presumed to be comparable to subatomic particles. They can pass through the earth easily, since ordinary matter is mostly empty space.

[johndevers@iprimus.com.au]

> Let us however give a more scientific answer
> and see how we could test this. If an appeciable fraction of the Earth/
> Sun is dark matter the Earth will be surrounded by a clould. This
> means that there is not an accurate inverse square law. Accurate
> orbital measurements show no trace of such an effect.


Does this mean we can throw away the idea of 10% of the dark matter
being made up of millicharged fermions as speculated on this site?

http://www.physorg.com/news136197792.html

in this paper?

Phys. Rev. D 77, 123503 (2008)


Should I assume millicharged fermions could lose energy?

[Ian Parker]

On 29 Jul, 02:43, p.br...@by.co.uk wrote:
> In article <00dd54c0-a0a9-4f7e-81d5-
> f9d692bf3...@x35g2000hsb.googlegroups.com>, ianpark...@gmail.com says...
>
> > The Earth cannot capture DM for one very simple reason. DM lands on
> > Earth at 11.2km/s + and comes out the other side at the same speed.
>
> > - Ian Parker
>
> If it was matter presumably it has mass? (isn't that the point?)
> A mass passing through the earth at "11.2 km/s +" would leave what size
> hole?
>
> Do I need to go out and buy a hat?
>
Neutinos pass through the Earth. This has been known for a long time.
The neutino's interactions are all weak nuclear. This dives it it's
enormous penetration.

The DM particles are NOT particles hitherto known. Reason at the Big
Bang hydrogen, Helium and Lithium were formed. Thermodynamics
therefore sets baryonic mass to about 4% Omega.

To explain DM we need new particles. Reason - Particles we know are
ruled out thermodynamically. The most popular particle is the "axion",
but there are other possibilities. Supersymmetry says that every Boson
is paired with a Fermion. We thus have a gravitino and a photino
pairing with gravitational waves and light respectively. These
Fermions have even less interaction with ordinary matter than the
neutrino. They have mass, yes, but that is all.

- Ian Parker

[johndevers@iprimus.com.au]

> The Earth cannot capture DM for one very simple reason. DM lands on
> Earth at 11.2km/s + and comes out the other side at the same speed.

Would tidal effects allow a small amount to get trapped?

[Thomas Smid]

On 27 Jul, 19:51, johndev...@iprimus.com.au wrote:
> If dark matter can't even escape the surface of the earth then why
> don't scientists include dark matter into their models and
> calculations of the mass of planets and stars?

Technically speaking, the earth does fully consist of dark matter, as
its mass can only be inferred from its gravity, but not from its
luminosity.

[Moderator's note: Of course, this is not the way in which the term
"dark matter" is normally understood. And, to be pedantic, while I
might not directly infer its mass, I certainly react with the Earth
every day, ultimately chemically. -P.H.]

Thomas

[Phillip Helbig---remove CLOTHES to reply]

In article <MPG.22f86362d0c59e1f9899bd@news.virginmedia.com>,
p.brane@by.co.uk writes:

> In article <00dd54c0-a0a9-4f7e-81d5-
> f9d692bf3f7d@x35g2000hsb.googlegroups.com>, ianparker2@gmail.com says...
>
> > The Earth cannot capture DM for one very simple reason. DM lands on
> > Earth at 11.2km/s + and comes out the other side at the same speed.
> >
> > - Ian Parker
>
> If it was matter presumably it has mass? (isn't that the point?)
> A mass passing through the earth at "11.2 km/s +" would leave what size
> hole?
>
> Do I need to go out and buy a hat?

If so, you should have noticed it already. A huge number of neutrinos
constantly pass through the Earth. Why isn't this more noticeable?
Because they interact only weakly with other matter (in fact, only via
the weak interaction---and, like everything, via gravity, but moving at
almost the speed of light, there is no chance of them getting caught).
Most dark-matter candidates would interact weakly with ordinary matter.
Since we know that dark matter is distributed differently than baryonic
matter, we know it can't be something which is more or less completely
captured by baryonic matter.

[p.brain@by.co.uk]

In article <g6nvmm$i76$1@online.de>, helbig@astro.multiCLOTHESvax.de
says...
> In article <MPG.22f86362d0c59e1f9899bd@news.virginmedia.com>,
> p.brane@by.co.uk writes:
>
> > In article <00dd54c0-a0a9-4f7e-81d5-
> > f9d692bf3f7d@x35g2000hsb.googlegroups.com>, ianparker2@gmail.com says...
> >
> > > The Earth cannot capture DM for one very simple reason. DM lands on
> > > Earth at 11.2km/s + and comes out the other side at the same speed.
> > >
> > > - Ian Parker
> >
> > If it was matter presumably it has mass? (isn't that the point?)
> > A mass passing through the earth at "11.2 km/s +" would leave what size
> > hole?
> >
> > Do I need to go out and buy a hat?
>
> If so, you should have noticed it already. A huge number of neutrinos
> constantly pass through the Earth. Why isn't this more noticeable?
> Because they interact only weakly with other matter (in fact, only via
> the weak interaction---and, like everything, via gravity, but moving at
> almost the speed of light, there is no chance of them getting caught).
> Most dark-matter candidates would interact weakly with ordinary matter.
> Since we know that dark matter is distributed differently than baryonic
> matter, we know it can't be something which is more or less completely
> captured by baryonic matter.
>
>
If I understand

Neutrinos have no charge and almost negligable mass and have not
been detected causing gravitational lensing, or any other physical effect
I'm aware of. Considering their abundance - pretty fortunate. I don't
think that analogy holds water.

OK so we are now saying that something that makes up so much of the
universe (75% ?) can't be detected because it only interacts weakly with
it.
Except it's interaction in the form of "gravity" is the presumed cause
for all manner of "interactions" otherwise inexplicable. Indeed
the very existance of dark matter is proposed because of gravitic effect
first noticed about 75 years ago.

And gravity requires - what - a pretty large amount of mass for
noticable effect.

Large amount of mass capable of moving galaxies X 11.2 km/s = ?
Getting caught shouldn't be an issue so much as digging holes in the
road?

I find it hard to have my cake and eat it here.
Or am I missing something?


-peter-

[Phillip Helbig---remove CLOTHES to reply]

In article <MPG.22f9bee7142d5ec4989a1c@news.virginmedia.com>,
p.brain@by.co.uk writes:

> Neutrinos have no charge and almost negligable mass and have not
> been detected causing gravitational lensing, or any other physical effect
> I'm aware of. Considering their abundance - pretty fortunate. I don't
> think that analogy holds water.

They CAN be detected, though as you point out they are difficult to
detect.

> OK so we are now saying that something that makes up so much of the
> universe (75% ?) can't be detected because it only interacts weakly with
> it.

Can't be detected EASILY. Yes.

> Except it's interaction in the form of "gravity" is the presumed cause
> for all manner of "interactions" otherwise inexplicable. Indeed
> the very existance of dark matter is proposed because of gravitic effect
> first noticed about 75 years ago.

Yes.

By the way, neutrinos aren't the dark matter, because they are hot (move
fast) whereas we know (from the comparison of observations to theories
of galaxy(-cluster) formation) that the dark matter is cold. It can't
be baryonic.

Put it this way---if it DID interact strongly with other stuff, then it
would be just more "normal matter". One has to be careful of
chauvinism, i.e. thinking that most of the universe is like us. We live
off the energy of the Sun, the planets formed together with the Sun, the
Sun has most of the mass of the solar system---so astronomy has,
historically, concentrated on luminous stuff (also for the practical
reason that it can be seen). However, a priori, there is no reason why
most matter shouldn't be dark. Similarly, one shouldn't be puzzled if
it doesn't interact much with our matter.

[Richard Saam]

Ian Parker wrote:
> On 29 Jul, 02:43, p.br...@by.co.uk wrote:
>> In article <00dd54c0-a0a9-4f7e-81d5-
>> f9d692bf3...@x35g2000hsb.googlegroups.com>, ianpark...@gmail.com says...
>>
>>> The Earth cannot capture DM for one very simple reason. DM lands on
>>> Earth at 11.2km/s + and comes out the other side at the same speed.
>>> - Ian Parker
>> If it was matter presumably it has mass? (isn't that the point?)
>> A mass passing through the earth at "11.2 km/s +" would leave what size
>> hole?
>>
>> Do I need to go out and buy a hat?
>>
> Neutinos pass through the Earth. This has been known for a long time.
> The neutino's interactions are all weak nuclear. This dives it it's
> enormous penetration.
>
> The DM particles are NOT particles hitherto known. Reason at the Big
> Bang hydrogen, Helium and Lithium were formed. Thermodynamics
> therefore sets baryonic mass to about 4% Omega.

There are two subjects here:

1. Big Bang Nucleosynthesis produced Hydrogen, Helium and Lithium in
'percentages' indicated by thermodynamics.

2. Total Big Bang Nucleosynthesis baryonic 'mass' is predicted by
thermodynamics to about 4% Omega.

One(1) has been verified spectrally by observing 'percentage'
concentrations in early starting materials for galactic formation.
There appears very little wiggle room for 'percentages' on one(1),
but where is the observational verification of total 'mass' on two(2)?

Richard Saam

>
> To explain DM we need new particles. Reason - Particles we know are
> ruled out thermodynamically. The most popular particle is the "axion",
> but there are other possibilities. Supersymmetry says that every Boson
> is paired with a Fermion. We thus have a gravitino and a photino
> pairing with gravitational waves and light respectively. These
> Fermions have even less interaction with ordinary matter than the
> neutrino. They have mass, yes, but that is all.
>
> - Ian Parker
>

[Richard Saam]

Phillip Helbig---remove CLOTHES to reply wrote:

> By the way, neutrinos aren't the dark matter, because they are hot (move
> fast) whereas we know (from the comparison of observations to theories
> of galaxy(-cluster) formation) that the dark matter is cold. It can't
> be baryonic.
>
Please explain:
'dark matter is cold therefore it can't be baryonic'

[Phillip Helbig---remove CLOTHES to reply]

In article <SHZjk.140614$102.132170@bgtnsc05-news.ops.worldnet.att.net>,
Richard Saam <rdsaam@att.net> writes:

> > Neutinos pass through the Earth. This has been known for a long time.
> > The neutino's interactions are all weak nuclear. This dives it it's
> > enormous penetration.
> >
> > The DM particles are NOT particles hitherto known. Reason at the Big
> > Bang hydrogen, Helium and Lithium were formed. Thermodynamics
> > therefore sets baryonic mass to about 4% Omega.
>
> There are two subjects here:
>
> 1. Big Bang Nucleosynthesis produced Hydrogen, Helium and Lithium in
> 'percentages' indicated by thermodynamics.
>
> 2. Total Big Bang Nucleosynthesis baryonic 'mass' is predicted by
> thermodynamics to about 4% Omega.
>
> One(1) has been verified spectrally by observing 'percentage'
> concentrations in early starting materials for galactic formation.
> There appears very little wiggle room for 'percentages' on one(1),
> but where is the observational verification of total 'mass' on two(2)?

The mass in stars is less than the predicted baryonic mass, the total
mass inferred, including dark matter, is much more. In addition to
stars, there is dark but baryonic matter, such as gas. This can be
observed via the Sunyaev-Zeldovich effect and, though it might not glow
optically, hot gas can be seen in X-rays.

There is a HUGE literature on estimates of various sorts of mass in
astrophysics; perhaps someone can suggest a recent review.

[Nicolaas Vroom]

"Thomas Smid" <thomas.smid@gmail.com> schreef in bericht
news:e741c177-38a3-4aa9-a397-b18de9e85944@y21g2000hsf.googlegroups.com...
> On 27 Jul, 19:51, johndev...@iprimus.com.au wrote:
>> If dark matter can't even escape the surface of the earth then why
>> don't scientists include dark matter into their models and
>> calculations of the mass of planets and stars?
>
> Technically speaking, the earth does fully consist of dark matter, as
> its mass can only be inferred from its gravity, but not from its
> luminosity.
>

I have a problem with this (I have read the note by the moderator)

Is not the whole idea behind the concept of dark matter that there is
not enough visible matter (Stars) including invisible matter in the form
of planets, pluto sized objects and planetoiden in the disc in order to
explain a ( any ?) galaxy rotation curve ?
As such we introduce a halo of dark matter mainly outside the disc
in the form of for example non baryonic particles.
See: http://en.wikipedia.org/wiki/Dark_matter Darkmatter composition.

If this reasoning is true than our planet does not consist of dark matter
At least not of the type of dark matter that constitutes 95% of our galaxy
(was 50%) See mentioned url.

> [Moderator's note: Of course, this is not the way in which the term
> "dark matter" is normally understood. >

Nicolaas Vroom
http://users.pandora.be/nicvroom/

[Gerry Quinn]

In article <cfb063c9-cf24-4703-9364-288e7237bac0
@w39g2000prb.googlegroups.com>, johndevers@iprimus.com.au says...

[bits snipped]

> If dark matter can't even escape the surface of the earth then why
> don't scientists include dark matter into their models and
> calculations of the mass of planets and stars?

> The speed of dark matter is about 6 miles per second (9km/s) Ref 1.

> Earth has an escape velocity of 11.2 km/s

First, a single lump of dark matter zooming towards the earth at 6 km
per second will accelerate as it falls, and thus will have enough energy
to go out the other side.

Also, if non-baryonic dark matter of unknown nature does in fact exist,
we don't know whether it forms lumps, as baryonic matter does. (Planets
and stars are examples of these lumps.)

It does seem to me, though, that if dark matter is lumpy like ordinary
matter, and is present in large quantities in the galaxy, then
gravitational interactions during the formation of stars should indeed
tend to cause the dark matter to end up mixed up with ordinary matter,
i.e. it should be present in large gravitationally condensed objects
such as stars and perhaps planets.

We can set limits on the extent to which this might be the case, though.
For example, the Earth clearly cannot be 50% dark matter, because we can
calculate the total density of the Earth by measuring the gravitational
constant. If it were 50% dark matter, then the average density of
normal matter in the Earth would be similar to that of uncompressed
surface minerals, which is impossible. Other more subtle anomalies
would be observable also.

It would be an interesting exercise to work out how much 'lumpy' dark
matter could be present without overstepping the bounds of what is
plausible based on known geophysical measurements. (Similarly for
stars, but I suspect this would be a more difficult analysis to make.)

Non-lumpy dark matter doesn't have the same problems - it might float
freely as a 'gas' pervading interstellar (or intergalactic) space.

- Gerry Quinn

[mathman]

Current ideas about dark matter seem to rule out any clumping. It is believed that it is made up of individual particles similar in size to fundamental particles, which don't interact in any way except gravity.

[Phillip Helbig---remove CLOTHES to reply]

In article <yF5kk.276596$SV4.138535@bgtnsc04-news.ops.worldnet.att.net>,
Richard Saam <rdsaam@att.net> writes:

> Phillip Helbig---remove CLOTHES to reply wrote:
>
> > By the way, neutrinos aren't the dark matter, because they are hot (move
> > fast) whereas we know (from the comparison of observations to theories
> > of galaxy(-cluster) formation) that the dark matter is cold. It can't
> > be baryonic.
> >
> Please explain:
> 'dark matter is cold therefore it can't be baryonic'

You added the "therefore". Two separate facts: it is cold, and it is
not baryonic.

[Phillip Helbig---remove CLOTHES to reply]

In article <sC3kk.106068$oo.49585@newsfe09.ams2>, "Nicolaas Vroom"
<nicolaas.vroom@pandora.be> writes:

> "Thomas Smid" <thomas.smid@gmail.com> schreef in bericht
> news:e741c177-38a3-4aa9-a397-b18de9e85944@y21g2000hsf.googlegroups.com...
> > On 27 Jul, 19:51, johndev...@iprimus.com.au wrote:
> >> If dark matter can't even escape the surface of the earth then why
> >> don't scientists include dark matter into their models and
> >> calculations of the mass of planets and stars?
> >
> > Technically speaking, the earth does fully consist of dark matter, as
> > its mass can only be inferred from its gravity, but not from its
> > luminosity.
>
> I have a problem with this (I have read the note by the moderator)
>
> Is not the whole idea behind the concept of dark matter that there is
> not enough visible matter (Stars) including invisible matter in the form
> of planets, pluto sized objects and planetoiden in the disc in order to
> explain a ( any ?) galaxy rotation curve ?

Yes, that is one of the original motivations. I believe the very first
motivation was a similar argument involving galaxy clusters, pointed out
by Fritz Zwicky: considering the velocities of the galaxies, the masses
inferred from the stars are not enough to keep the cluster bound.

[Richard Saam]

Phillip Helbig---remove CLOTHES to reply wrote:
> In article <yF5kk.276596$SV4.138535@bgtnsc04-news.ops.worldnet.att.net>,
> Richard Saam <rdsaam@att.net> writes:
>
>> Phillip Helbig---remove CLOTHES to reply wrote:
>>
>>> By the way, neutrinos aren't the dark matter, because they are hot (move
>>> fast) whereas we know (from the comparison of observations to theories
>>> of galaxy(-cluster) formation) that the dark matter is cold. It can't
>>> be baryonic.
>>>
>> Please explain:
>> 'dark matter is cold therefore it can't be baryonic'
>
> You added the "therefore". Two separate facts: it is cold, and it is
> not baryonic.

Indications (not facts) of dark matter as 'cold' and 'non baryonic'
are based on thermodynamic "'theories' of galaxy(-cluster) formation"
What are the observations in these 'galaxy(-cluster) formations' that
support this 'dark matter' theory to the exclusion of others such as the
theory: "dark matter is hot and/or dark matter is baryonic?

What temperatures quantitatively describe 'hot' and 'cold'?

[mathman]

"dark matter is hot and/or dark matter is baryonic?

Dark matter being cold is based on surmised distribution based on gravitational effect. If it were hot it would move around much more.\ and thus be more uniform.

Dark matter being non-baryonic is inferred from observed deuterium (and other light nuclei) distribution. This distribution gives an estimate of the amount of baryonic matter, which is much too small to account for the gravitational effects observed.

[Phillip Helbig---remove CLOTHES to reply]

In article <lzDlk.287061$SV4.117136@bgtnsc04-news.ops.worldnet.att.net>,
Richard Saam <rdsaam@att.net> writes:

> >> Please explain:
> >> 'dark matter is cold therefore it can't be baryonic'
> >
> > You added the "therefore". Two separate facts: it is cold, and it is
> > not baryonic.
>
> Indications (not facts) of dark matter as 'cold' and 'non baryonic'
> are based on thermodynamic "'theories' of galaxy(-cluster) formation"

We have a good upper limit on the baryon density from nuclear synthesis.
Unless you believe in MOND or something, just the observation of bound
systems like galaxies and galaxy clusters lead to dark matter---no
thermodynamic theories (except the virial theorem) nor gastrophysics
required.

> What are the observations in these 'galaxy(-cluster) formations' that
> support this 'dark matter' theory to the exclusion of others such as the
> theory: "dark matter is hot and/or dark matter is baryonic?

The nucleosynthesis limit means it can't be baryonic. It can't be hot
because then structure would form from the top down, whereas it forms
from the bottom up.

> What temperatures quantitatively describe 'hot' and 'cold'?

Hot means that it is not gravitatationally bound in mass concentrations
and can thus smooth these out. However, we OBSERVE that small
structures like galaxies form before large structures like
superclusters. This is incompatible with hot dark matter.

[Oh No]

Thus spake Phillip Helbig---remove CLOTHES to reply <helbig@astro.multiC
LOTHESvax.de>
>In article <yF5kk.276596$SV4.138535@bgtnsc04-news.ops.worldnet.att.net>,
>Richard Saam <rdsaam@att.net> writes:
>
>> Phillip Helbig---remove CLOTHES to reply wrote:
>>
>> > By the way, neutrinos aren't the dark matter, because they are hot (move
>> > fast) whereas we know (from the comparison of observations to theories
>> > of galaxy(-cluster) formation) that the dark matter is cold. It can't
>> > be baryonic.
>> >
>> Please explain:
>> 'dark matter is cold therefore it can't be baryonic'
>
>You added the "therefore". Two separate facts: it is cold, and it is
>not baryonic.
>
If it were baryonic, it would interact via the e.m force. Ergo it would
not be cold. (this is the meaning of cold, therefore is correct).

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex

[Oh No]

Thus spake Thomas Smid <thomas.smid@gmail.com>
>On 27 Jul, 19:51, johndev...@iprimus.com.au wrote:
>> If dark matter can't even escape the surface of the earth then why
>> don't scientists include dark matter into their models and
>> calculations of the mass of planets and stars?
>
>Technically speaking, the earth does fully consist of dark matter, as
>its mass can only be inferred from its gravity, but not from its
>luminosity.
>
>[Moderator's note: Of course, this is not the way in which the term
>"dark matter" is normally understood.

This is the distinction between dark matter, which is precisely as
Thomas says, and cold dark matter, which is what you are thinking of. As
this is explained in many text books, I would say that this is how
ordinary dark matter should normally be understood. It does not do to
confuse it with cold dark matter, which is exotic.

To answer the OP's question, assuming he does mean cold dark matter, the
density of matter in space, including the density of cold dark matter,
is extremely low compared to the density of the earth, or even compared
to the density of the solar system. The contribution of CDM to such
small systems is effectively negligible.

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex

[Oh No]

Thus spake Richard Saam <rdsaam@att.net>
>Phillip Helbig---remove CLOTHES to reply wrote:
>> In article <yF5kk.276596$SV4.138535@bgtnsc04-news.ops.worldnet.att.net>,
>> Richard Saam <rdsaam@att.net> writes:
>>
>>> Phillip Helbig---remove CLOTHES to reply wrote:
>>>
>>>> By the way, neutrinos aren't the dark matter, because they are hot (move
>>>> fast) whereas we know (from the comparison of observations to theories
>>>> of galaxy(-cluster) formation) that the dark matter is cold. It can't
>>>> be baryonic.
>>>>
>>> Please explain:
>>> 'dark matter is cold therefore it can't be baryonic'
>>
>> You added the "therefore". Two separate facts: it is cold, and it is
>> not baryonic.
>
>Indications (not facts) of dark matter as 'cold' and 'non baryonic'
>are based on thermodynamic "'theories' of galaxy(-cluster) formation"
>What are the observations in these 'galaxy(-cluster) formations' that
>support this 'dark matter' theory to the exclusion of others such as the
>theory: "dark matter is hot and/or dark matter is baryonic?

Can I recommend Andrew Liddle, and Introduction to Modern Cosmology, who
explains this in very easy terms. We do have observations which place
clear bounds on the density of baryonic matter.

>
>What temperatures quantitatively describe 'hot' and 'cold'?

It is not a matter of temperature, so much as failure to interact via
the e.m. force, hence no radiation spectrum.

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex

[Boris Borcic]

Phillip Helbig---remove CLOTHES to reply wrote:
>
> By the way, neutrinos aren't the dark matter, because they are hot (move
> fast)

Would you care to expand on this a little ? Do we know they are hot as a whole,
because of our theory of their origin, or is it the case that experiments have
been devised to detect slow neutrinos (of mysterious origin) with de Broglie
wavelengths of interstellar scale, and failed to observe them ? And do the
properties of neutrinos forbid the coexistence of thermodynamically distinct
populations ?

Cheers, BB

[Oh No]

Thus spake Boris Borcic <bborcic@gmail.com>
>Phillip Helbig---remove CLOTHES to reply wrote:
>> By the way, neutrinos aren't the dark matter, because they are hot
>>(move fast)

Neutrinos are dark matter, but not cold dark matter.

>Would you care to expand on this a little ? Do we know they are hot as
>a whole, because of our theory of their origin, or is it the case that
>experiments have been devised to detect slow neutrinos (of mysterious
>origin) with de Broglie wavelengths of interstellar scale, and failed
>to observe them ? And do the properties of neutrinos forbid the
>coexistence of thermodynamically distinct populations ?

No, it is a part of what we mean by "cold dark matter". Cold dark matter
is intrinsically cold. Neutrinos have the property that they can be hot.
We can calculate the density of the neutrinos emanating from the big
bang, and even with the most generous estimate of neutrino mass, there
are not sufficient to account for the observed mass density of the
universe.

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex

[Boris Borcic]

Oh No wrote:
> Thus spake Boris Borcic <bborcic@gmail.com>
>> Phillip Helbig---remove CLOTHES to reply wrote:
>>> By the way, neutrinos aren't the dark matter, because they are hot
>>> (move fast)
>
> Neutrinos are dark matter, but not cold dark matter.
>
>> Would you care to expand on this a little ? Do we know they are hot as
>> a whole, because of our theory of their origin, or is it the case that
>> experiments have been devised to detect slow neutrinos (of mysterious
>> origin) with de Broglie wavelengths of interstellar scale, and failed
>> to observe them ? And do the properties of neutrinos forbid the
>> coexistence of thermodynamically distinct populations ?
>
> No, it is a part of what we mean by "cold dark matter". Cold dark matter
> is intrinsically cold. Neutrinos have the property that they can be hot.
> We can calculate the density of the neutrinos emanating from the big
> bang, and even with the most generous estimate of neutrino mass, there
> are not sufficient to account for the observed mass density of the
> universe.

Mh. Far from me to deny the cosmology here. And I understand the idea that
nearly massless neutrinos will typically move nearly like massless particles.

But still the fact that neutrinos have rest mass, makes slow neutrinos
physically possible in principle. And I don't understand why no one ever
attempts the exercize to paint abstract systems featuring slow neutrinos
-before- stating that they can't play a role in the real world. Or even after.
Sure the minutest amount of kinetic energy will have them zip fast, but otoh
they almost don't interact so that a neutrino can be "stably cold", can it not ?

Maybe it is because my schooling in QM aborted quite early - ie not much further
than the Bohr atom - but it strikes me that the de Broglie wavelength for
neutrinos at slow CDM speeds implied by current rest mass guesstimates is on the
scale of light-days if I am not mistaken. That is, a wavelength such that the
type of argumentation applied to doctor the model of a solar system to get the
Bohr atom, should be transposable to the case of a neutrino gravitating "around"
a real celestial body, with orbital parameters consistent with a solar system
(or nearly so). The fun of it should be sufficient motivation for such a
transposition, even without any expectation of actually observing such a system.
The issue is actually more than fun, it has to do with testing theorical devices
wherever they seem applicable or else justify a difference in applicability.

Cheers, BB

[Phillip Helbig---remove CLOTHES to reply]

In article <48981768$1_4@news.bluewin.ch>, Boris Borcic
<bborcic@gmail.com> writes:

> > By the way, neutrinos aren't the dark matter, because they are hot (move
> > fast)
>
> Would you care to expand on this a little ? Do we know they are hot as a whole,
> because of our theory of their origin, or is it the case that experiments have
> been devised to detect slow neutrinos (of mysterious origin) with de Broglie
> wavelengths of interstellar scale, and failed to observe them ? And do the
> properties of neutrinos forbid the coexistence of thermodynamically distinct
> populations ?

Don't know about stuff of "mysterious origin", but the mass limits on
known neutrino sources imply that they are "hot".

[johndevers@iprimus.com.au]

I noticed that someone recently measured how much dark matter was in
the solar system, how does the dark matter travelling at 9km/s lose
enough energy to get trapped in our solar system?

http://www.universetoday.com/2008/06/26/dark-matter-is-denser-in-the-solar-=
system/

"Dark matter isn't just far off in the Milky Way or somewhere on the
other side of the Universe, though: it's right here at home in our
Solar System. In a recent paper submitted to Physical Review D, Ethan
Siegel and Xiaoying Xu of the University of Arizona analyzed the
distribution of dark matter in our Solar System, and found that the
mass of dark matter is 300 times more than that of the galactic halo
average, and the density is 16,000 times higher than that of the
background dark matter."

"Over the history of the Solar System, Xu and Siegel calculate that
1.07 X 10^20 kg of dark matter have been captured, or about 0.0018%
the mass of the Earth. To get a handle on this number, the mass of
Ceres =96 the largest object in the asteroid belt between Mars and
Jupiter =96 is about 9 times this amount."

[Oh No]

Thus spake Boris Borcic <bborcic@gmail.com>
>Mh. Far from me to deny the cosmology here. And I understand the idea
>that nearly massless neutrinos will typically move nearly like massless
>particles.

yes
>
>But still the fact that neutrinos have rest mass, makes slow neutrinos
>physically possible in principle.

Indeed, but they would not be what we call "CDM"

> And I don't understand why no one ever attempts the exercize to paint
>abstract systems featuring slow neutrinos -before- stating that they
>can't play a role in the real world.

But they do. The calculation is done for all neutrinos. We
do not distinguish neutrinos by temperature.

>Or even after. Sure the minutest amount of kinetic energy will have
>them zip fast, but otoh they almost don't interact so that a neutrino
>can be "stably cold", can it not ?
>
>Maybe it is because my schooling in QM aborted quite early - ie not
>much further than the Bohr atom - but it strikes me that the de Broglie
>wavelength for neutrinos at slow CDM speeds implied by current rest
>mass guesstimates is on the scale of light-days if I am not mistaken.
>That is, a wavelength such that the type of argumentation applied to
>doctor the model of a solar system to get the Bohr atom, should be
>transposable to the case of a neutrino gravitating "around" a real
>celestial body, with orbital parameters consistent with a solar system
>(or nearly so). The fun of it should be sufficient motivation for such
>a transposition, even without any expectation of actually observing
>such a system. The issue is actually more than fun, it has to do with
>testing theorical devices wherever they seem applicable or else justify
>a difference in applicability.
>
Calculations on CDM are done from cosmological information, not just
from galaxy rotation curves.


Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex

[johndevers@iprimus.com.au]

How does dark matter lose enough energy for our solar system to have
300 times the density of the galactic halo dark matter?

Can it clump just using gravity and not losing energy in any other
way?

http://www.universetoday.com/2008/06/26/dark-matter-is-denser-in-the-solar-system/


Dark matter was theorized to exist relatively recently, and we've come
a long way in understanding what makes up a whopping 23% of our
Universe. Our own galaxy is surrounded by a halo of dark matter that
adds to its mass. A recent paper on the dark matter closer to home –
right here in our own Solar System – reveals that it is denser and
more massive than in the galactic halo.
Dark matter is just plain weird stuff. It doesn't give off light, has
mass and reacts gravitationally with "normal" matter – the stuff that
we and our planet and the stars are composed of. Just like normal
matter, it "clumps" up, or accretes, because of this gravitational
attraction; we find more dark matter near galaxies than in the vast
expanses between them.
Dark matter isn't just far off in the Milky Way or somewhere on the
other side of the Universe, though: it's right here at home in our
Solar System. In a recent paper submitted to Physical Review D, Ethan
Siegel and Xiaoying Xu of the University of Arizona analyzed the
distribution of dark matter in our Solar System, and found that the
mass of dark matter is 300 times more than that of the galactic halo
average, and the density is 16,000 times higher than that of the
background dark matter.
Over the history of the Solar System, Xu and Siegel calculate that
1.07 X 10^20 kg of dark matter have been captured, or about 0.0018%
the mass of the Earth. To get a handle on this number, the mass of
Ceres – the largest object in the asteroid belt between Mars and
Jupiter – is about 9 times this amount.
Siegel and Xu calculated how much dark matter the Solar System has
swept up over it's 4.5 billion-year lifespan by modeling the
composition of the background dark matter halo in the orbit of the
Solar System around the galaxy, and calculating just how much dark
matter would be trapped by the Solar System as it moves through this
halo. They ran this calculation for the Sun and each one of the eight
planets separately, giving the distribution of the matter throughout
the Solar System, as well as the total amount captured.
Much like when you drive your car through a light snowfall, dark
matter "sticks" to the Solar System when it is gravitationally bound
by the Sun and planets. Just as some of the snow melts on your
windshield (hopefully), some doesn't stick to the hood and most just
flies right by, dark matter isn't distributed evenly throughout our
Solar System, either. Some planets have more dark matter surrounding
them than others, depending on where they are. Shown below is the
density distribution of the dark matter in the Solar System

The first spike is Mercury, and the next two spikes are Venus and
Earth (Mars doesn't show up). The next is Jupiter, followed by a small
bump from Saturn and finally Uranus and Neptune combined create the
last small bump.
How does the local dark matter effect interactions in the Solar
System? Well,it doesn't have a large effect on the orbits of the
planets, nor does it slow down the Solar System in its orbit around
the galactic center appreciably.
"Planetary orbits, if there were enough dark matter present, would
have their perihelia precess faster than if there were no dark matter.
The amount of dark matter allowed from these observations is
considerably greater than the amount I predict. The errors on the
measurements of perihelion precession are in units of hundredths of an
arc second per century…Even if you assume the dark matter is at rest
with respect to the galaxy that the Solar System moves through (which
is the extreme example), the Sun is of order 10^30 kg; capturing a
10^20 kg clump of dark matter will slow you down by about 20 microns/
second over the lifetime of the Solar System. So that would be small."
– Ethan Siegel in an email interview.
And, alas, the mystery of the Pioneer anomaly is not going to be
solved by this revelation, as the mass of the captured dark matter is
not enough to explain the odd motions of that spacecraft.
The discovery of a higher density and mass of dark matter in our
neighborhood may aid in the study and detection of dark matter,
though. Knowing the mass and density distribution of the local dark
matter – and thus knowing how much and where to look for it – will
provide astronomers looking into solving exactly what it's made up of
with more information .
"Our determination of the local dark matter density and velocity
distribution are of great importance to direct detection experiments.
The most recent calculations that have been carried out assume that
the properties of dark matter at the Sun's location are derived
directly from the galactic halo. By comparison, we find that
terrestrial experiments should also consider a component of dark
matter with a density 16,000 times greater than the background halo
density," wrote Xu and Siegel.

[johndevers@iprimus.com.au]

I have noticed a couple more articles about dark matter recently that
imply a loss of angular momentum.


Can dark matter lose angular momentum when being "scattered" or
"repelled" by baryonic matter?


http://www.universetoday.com/2008/03/08/greedy-supermassive-black-holes-dislike-dark-matter/


“Dark matter is predicted to be collisionless and will be scattered
very easily by baryonic gas clouds and stars. It seems unlikely that
dark matter will be able to stay inside the black hole's accretion
disk for very long before it is repelled by all the "normal" matter
being pulled toward the event horizon.”



How do you explain a dark matter density that is “200 billion times
larger than the galactic halo density” and is predicted between the
Earth and the Moon without dark matter losing angular momentum?


http://www.telegraph.co.uk/earth/main.jhtml?view=DETAILS&grid=&xml=/earth/2008/09/23/scidarkmatter123.xml



"This upper bound (based only on the gravitational action of dark
matter on the moon, Earth, asteroids, and satellites) is very weak -
it allows dark matter densities near Earth that are 200 billion times
larger than the galactic halo density," adds Dr Adler.



Why do the Pamela astronomers think that dark matter smashes itself
apart, I wonder how it does that without losing angular momentum?


http://www.timesonline.co.uk/tol/news/uk/article4794826.ece

“The observation fitted predictions that dark matter would be
concentrated in galactic cores becoming so dense that particles
collide and smash each other apart, emitting positrons.”

[Phillip Helbig---remove CLOTHES to reply]

In article
<6d2d686c-d9cb-497e-8e4a-002d162a7c51@b38g2000prf.googlegroups.com>,
johndevers@iprimus.com.au writes:

> How do you explain a dark matter density that is 200 billion times
> larger than the galactic halo density and is predicted between the
> Earth and the Moon without dark matter losing angular momentum?
>
> http://www.telegraph.co.uk/earth/main.jhtml?view=DETAILS&grid=&xml=/earth/2008/09/23/scidarkmatter123.xml
>
> "This upper bound (based only on the gravitational action of dark
> matter on the moon, Earth, asteroids, and satellites) is very weak -
> it allows dark matter densities near Earth that are 200 billion times
> larger than the galactic halo density," adds Dr Adler.

Note that an upper limit is not the same thing as a prediction. I'm
pretty sure that no-one has predicted a dark-matter density 200 billion
times as high as the galactic-halo density.

The average density of the universe is about a hydrogen atom per cubic
meter. 200 billion hydrogen atoms per cubic meter is still a very good
vacuum. Thus, it's no surprise that solar-system physics doesn't set a
very strong upper limit. Similarly, the cosmological constant ("dark
energy" in modern parlance, though I prefer the name "smooth tension"),
based only on solar-system observations, could be much larger than we
observe it to be based on extragalactic observations.