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dark matter hypothesis



 
 
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  #1  
Old November 26th 18, 07:49 PM posted to sci.astro.research
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Default dark matter hypothesis

aIs it possible that the missing mass, the 'dark matter',
consists of two generations of burned out stars?
These would be short lifetimes, hence large masses,
according to star formation theory, hence mostly black holes
or neutron stars. I don't see that as a problem.

What are the counter-arguments?

--
Rich

[[Mod. note -- Microlensing studies show that at most a small fraction
of the dark matter in the Milky Way's halo can be in compact objects
of stellar mass. For example, the EROS project
https://arxiv.org/abs/astro-ph/0607207
concluded that "machos in the mass range 0.6e-7 M_sun M 15 M_sun
are ruled out as the primary occupants of the Milky Way Halo".

I don't know offhand what (if any) limits there are for M31 or maybe
other galaxies.
-- jt]]
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  #2  
Old November 27th 18, 08:03 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Posts: 244
Default dark matter hypothesis

In article ,
writes:

aIs it possible that the missing mass, the 'dark matter',
consists of two generations of burned out stars?


No.

These would be short lifetimes, hence large masses,
according to star formation theory, hence mostly black holes
or neutron stars. I don't see that as a problem.

What are the counter-arguments?


There are several.

[[Mod. note -- Microlensing studies show that at most a small fraction
of the dark matter in the Milky Way's halo can be in compact objects
of stellar mass. For example, the EROS project
https://arxiv.org/abs/astro-ph/0607207
concluded that "machos in the mass range 0.6e-7 M_sun M 15 M_sun
are ruled out as the primary occupants of the Milky Way Halo".


Right.

I don't know offhand what (if any) limits there are for M31 or maybe
other galaxies.
-- jt]]


I was co-author on a paper which pointed out that a significant fraction
of dark matter can't be on compact objects between us and quasars (i.e.
in most of the observable universe), otherwise this would be seen in
quasar light curves (which, despite some claims to the contrary, is not
the case):

http://www.astro.multivax.de:8000/he...sing_qsos.html
http://adsabs.harvard.edu/abs/2003A&A...408...17Z

[[Mod. note -- URL corrected with author's permission. -- jt]]

Also, big-bang nucleosynthesis tells us what fraction of the universe is
in baryons; there is no way that stars, being baryonic, could make up a
significant fraction of dark matter.
  #3  
Old November 28th 18, 06:43 AM posted to sci.astro.research
jacobnavia
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Posts: 101
Default dark matter hypothesis

Le 26/11/2018 à 19:49, a écrit :
[[Mod. note -- Microlensing studies show that at most a small fraction
of the dark matter in the Milky Way's halo can be in compact objects
of stellar mass. For example, the EROS project
https://arxiv.org/abs/astro-ph/0607207
concluded that "machos in the mass range 0.6e-7 M_sun M 15 M_sun
are ruled out as the primary occupants of the Milky Way Halo".


That study assumes a spherical halo around the galaxy. It measures the
events when a massive body passes between us and stars in the small and
large maghellanic clouds, two satellite galaxies of our own galaxy.

IF the halo is spherical THEN the study is right.

If the halo is NOT spherical but follows the plane of the milky way,
i.e. most dead stars are in the galaxy plane and WITHIN the galaxy, that
study proves nothing.

If we suppose that the galaxy is old, very old, a lot of star corpses
should be around within the plane of the galaxy where they spent all
their relatively short lives...

Now, most stars that go supernovae have non-symmetrical explosions that
could propel their "dead" corpses in random directions, but the galaxy's
gravity should hold most of them back and keep them within the galaxy
plane.

To prove/disprove this hypothesis we should look for einstein rings
within our own galaxy.

  #4  
Old November 28th 18, 06:43 AM posted to sci.astro.research
[email protected]
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Posts: 6
Default dark matter hypothesis

On November 27, Phillip Helbig (undress to reply) wrote:
Is it possible that the missing mass, the 'dark matter',
consists of two generations of burned out stars?
These would be short lifetimes, hence large masses,
according to star formation theory, hence mostly black holes
or neutron stars. I don't see that as a problem.
What are the counter-arguments?


There are several.

[[Mod. note -- Microlensing studies show that at most a small fraction
of the dark matter in the Milky Way's halo can be in compact objects
of stellar mass. For example, the EROS project
https://arxiv.org/abs/astro-ph/0607207
concluded that "machos in the mass range 0.6e-7 M_sun M 15 M_sun
are ruled out as the primary occupants of the Milky Way Halo".


Right.
I was co-author on a paper which pointed out that a significant fraction
of dark matter can't be on compact objects between us and quasars (i.e.
in most of the observable universe), otherwise this would be seen in
quasar light curves (which, despite some claims to the contrary, is not
the case):

http://www.astro.multivax.de:8000/he...sing_qsos.html
http://adsabs.harvard.edu/abs/2003A&A...408...17Z


I'm unfamiliar with this technique - microlensing refers
to the occlusion of distant bright objects, by nearer objects?
Thus gravitational lensing effects?

I don't understand the primacy of the masses.
Wouldn't the statistics depend on the volume of
the 'dark' objects? That is, their solid angle arc,
how much of the sky they cover?

I don't find the reasoning compelling. You looked
at quasar variability, and concluded that MACHO
doesn't explain it. Isn't it a big leap to say such
objects don't exist at all?

Also, big-bang nucleosynthesis tells us what fraction of the universe
is in baryons; there is no way that stars, being baryonic, could make
up a significant fraction of dark matter.


Seeing that 80% of the mass of the mass is 'missing', of
unknown character, all such origin theories are suspect.

--
Rich

  #5  
Old November 28th 18, 07:44 AM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 244
Default dark matter hypothesis

In article , jacobnavia
writes:

That study assumes a spherical halo around the galaxy. It measures the
events when a massive body passes between us and stars in the small and
large maghellanic clouds, two satellite galaxies of our own galaxy.

IF the halo is spherical THEN the study is right.


There is much evidence that galactic halos are spherical.

If the halo is NOT spherical but follows the plane of the milky way,
i.e. most dead stars are in the galaxy plane and WITHIN the galaxy,
that study proves nothing.


Note that there are similar studies lucking along the plane of the
galaxy towards the bulge. Same result: the bulk of the dark matter
cannot be in compact objects of around a solar mass.

If we suppose that the galaxy is old, very old,


Older than it is normally thought to be? On what grounds?

a lot of star corpses
should be around within the plane of the galaxy where they spent all
their relatively short lives...


Star corpses are baryonic, and hence ruled out due to upper limits on
the total amount of baryons.

To prove/disprove this hypothesis we should look for einstein rings
within our own galaxy.


One won't see Einstein rings, since a) they are too small and b) occur
only when there is (nearly) perfect alignment. Rather, such
microlensing surveys look for the brightening then dimming of background
objects caused by the gravitational-lensing effect when they pass near
the line of sight of a foreground object
  #6  
Old November 28th 18, 07:48 AM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 244
Default dark matter hypothesis

In article ,
writes:

I'm unfamiliar with this technique - microlensing refers
to the occlusion of distant bright objects, by nearer objects?
Thus gravitational lensing effects?


Yes. Not necessary occlusion, though; it's enough if a background
object is near the line of sight to a foreground object. Due to proper
motion, the proximity changes with time, and since the amplification
depends on the radial distance, one sees a typical brightening then
dimming of the background object.

[[Mod. note -- To the original poster (and anyone else unfamiliar
with the technique): The Wikipedia article
https://en.wikipedia.org/wiki/Gravit...l_microlensing
is an excellent introduction.
-- jt]]

I don't understand the primacy of the masses.
Wouldn't the statistics depend on the volume of
the 'dark' objects? That is, their solid angle arc,
how much of the sky they cover?


Not so much their own solid angle, but rather the solid angle within
which an appreciable gravitational-lensing effect occurs.

I don't find the reasoning compelling. You looked
at quasar variability, and concluded that MACHO
doesn't explain it. Isn't it a big leap to say such
objects don't exist at all?


The conclusion is not that they don't exist at all, but rather that
they cannot explain most of the long-term variability of quasars.
This contradicts a claim that most long-term variability of quasars
is due to microlensing, which in turn would imply that they make
up at least most of the dark matter in the universe. Executive
summary: Yes, at first glance long-term quasar variability is
compatible with microlensing, if one looks at individual light
curves. However, this hypothesis makes predictions about the
distribution of amplifications which are in conflict with
observations.

Also, big-bang nucleosynthesis tells us what fraction of the universe
is in baryons; there is no way that stars, being baryonic, could make
up a significant fraction of dark matter.


Seeing that 80% of the mass of the mass is 'missing', of
unknown character, all such origin theories are suspect.


Why? If you have a theory which predicts what all the matter in
the universe is composed of, let us know. Otherwise, we discover
it, component by component. We know more about some components
than about others. For example, we know how many baryons there can
be at most. This is not enough to explain most of the dark matter,
so there must be some other component. What is surprising or suspect
about that?

If one thinks that dark matter is somehow strange, one assumes, for
no good reason, that all components of the mass of the universe
must be detectable via our senses, or by astronomical techniques
at the stage they were during the second half of the twentieth
century.
  #7  
Old November 28th 18, 09:49 PM posted to sci.astro.research
Richard D. Saam
external usenet poster
 
Posts: 234
Default dark matter hypothesis

On 11/27/18 1:03 PM, Phillip Helbig (undress to reply) wrote:
In article ,
writes:

aIs it possible that the missing mass, the 'dark matter',
consists of two generations of burned out stars?


No.

These would be short lifetimes, hence large masses,
according to star formation theory, hence mostly black holes
or neutron stars. I don't see that as a problem.

What are the counter-arguments?


There are several.

[[Mod. note -- Microlensing studies show that at most a small fraction
of the dark matter in the Milky Way's halo can be in compact objects
of stellar mass. For example, the EROS project
https://arxiv.org/abs/astro-ph/0607207
concluded that "machos in the mass range 0.6e-7 M_sun M 15 M_sun
are ruled out as the primary occupants of the Milky Way Halo".


Right.

I don't know offhand what (if any) limits there are for M31 or maybe
other galaxies.
-- jt]]


I was co-author on a paper which pointed out that a significant fraction
of dark matter can't be on compact objects between us and quasars (i.e.
in most of the observable universe), otherwise this would be seen in
quasar light curves (which, despite some claims to the contrary, is not
the case):

http://www.astro.multivax.de:8000/he...sing_qsos.html
http://adsabs.harvard.edu/abs/2003A&A...408...17Z

[[Mod. note -- URL corrected with author's permission. -- jt]]

Also, big-bang nucleosynthesis tells us what fraction of the universe is
in baryons; there is no way that stars, being baryonic, could make up a
significant fraction of dark matter.


The Big-bang nucleosynthesis hypothesis does not warrant
such an absolute telling baryon fraction statement
in terms of on going BBN mechanistic derivation efforts
https://arxiv.org/abs/1810.05976v2
RDS

  #8  
Old November 30th 18, 11:16 PM posted to sci.astro.research
Nicolaas Vroom
external usenet poster
 
Posts: 213
Default dark matter hypothesis

On Wednesday, 28 November 2018 21:49:18 UTC+1, Richard D. Saam wrote:
On 11/27/18 1:03 PM, Phillip Helbig (undress to reply) wrote:

Also, big-bang nucleosynthesis tells us what fraction of the universe is
in baryons; there is no way that stars, being baryonic, could make up a
significant fraction of dark matter.


The Big-bang nucleosynthesis hypothesis does not warrant
such an absolute telling baryon fraction statement
in terms of on going BBN mechanistic derivation efforts
https://arxiv.org/abs/1810.05976v2
RDS


This interesting (up to date) article mentions the word baryonic,
however nothing about darkmatter and baryon fraction.

[Moderator's note: Since we have a pretty good idea of the total
density, the difference between that and the baryonic density is the
dark-matter density, more or less by definition. -P.H.]

At the beginning of the article we reed: "Nevertheless, it is physics
that needs to be considered in any calculation of BBN."
I agree if you want to understand the early evolution of the universe
it is physics.
At the end we read: "The revised abundances exacerbate the deviation
of BBN etc perhaps suggesting a crucial greater need for new physics
and/or astrophysical explanations."
My interpretation is that the birth of non-baryonic matter is not part
BBN and started later.

[Moderator's note: We don't know what dark matter is, but as far as I
know there is no plausible scenario where it forms after BBN. -P.H.]

Secondly any explanation requires a definition what darkmatter
(i.e. non-baryonic matter) physical is.

[Moderator's note: He whatever is not baryonic. -P.H.]

The title of the article https://arxiv.org/abs/astro-ph/0501171 is:
"Detection of the Baryon Acoustic Peak in the Large-Scale
Correlation Function of SDSS Luminous Red Galaxies"
Baryon fraction = Omegab/Omagam is dicussed at page 2.
Here we read:
"A simple way to understand this is to consider that from an initial
point perturbation common to the dark matter and the baryons,
the dark matter perturbation grows in place while the baryonic
perturbation is carried outward in an expanding spherical wave"
IMO this is not simple.

[Moderator's note: While the process is relatively simple compared to
some other things, what is meant is that this is an easy-to-understand
rough sketch, not that the entire process is extremely simple. -P.H.]

Nicolaas Vroom

  #9  
Old December 2nd 18, 12:00 AM posted to sci.astro.research
Richard D. Saam
external usenet poster
 
Posts: 234
Default dark matter hypothesis

On 11/30/18 4:16 PM, Nicolaas Vroom wrote:
On Wednesday, 28 November 2018 21:49:18 UTC+1, Richard D. Saam wrote:
On 11/27/18 1:03 PM, Phillip Helbig (undress to reply) wrote:

Also, big-bang nucleosynthesis tells us what fraction of the universe is
in baryons; there is no way that stars, being baryonic, could make up a
significant fraction of dark matter.


The Big-bang nucleosynthesis hypothesis does not warrant
such an absolute telling baryon fraction statement
in terms of on going BBN mechanistic derivation efforts
https://arxiv.org/abs/1810.05976v2
RDS


This interesting (up to date) article mentions the word baryonic,
however nothing about darkmatter and baryon fraction.

[Moderator's note: Since we have a pretty good idea of the total
density, the difference between that and the baryonic density is the
dark-matter density, more or less by definition. -P.H.]


[Moderator's note: Quoted text snipped. -P.H.]

Ref 1 https://arxiv.org/abs/1810.05976v2
Ref 2 https://arxiv.org/abs/1811.04932
There was a very vigorous response[2] to [1]
defending the current BBN calculation
"The detailed and correct computation
of big-bang nucleosynthesis (BBN) dates
back 51 years to the seminal papers of Wagoner, Fowler and Hoyle"
(also referenced in 1)
but in their conclusions[2];
"We have not been able to identify
the source of the discrepancy with [1]"

Apparently it comes down to:
How do BBN classical Maxwell-Boltzmann plasma
baryon relativistic velocity distributions
affect nuclear reaction rates?
rds

  #10  
Old December 7th 18, 07:13 AM posted to sci.astro.research
Martin Brown[_2_]
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Posts: 4
Default dark matter hypothesis

On 01/12/2018 23:00, Richard D. Saam wrote:
On 11/30/18 4:16 PM, Nicolaas Vroom wrote:
On Wednesday, 28 November 2018 21:49:18 UTC+1, Richard D. Saam wrote:
On 11/27/18 1:03 PM, Phillip Helbig (undress to reply) wrote:

Also, big-bang nucleosynthesis tells us what fraction of the universe is
in baryons; there is no way that stars, being baryonic, could make up a
significant fraction of dark matter.

The Big-bang nucleosynthesis hypothesis does not warrant
such an absolute telling baryon fraction statement
in terms of on going BBN mechanistic derivation efforts
https://arxiv.org/abs/1810.05976v2
RDS


This interesting (up to date) article mentions the word baryonic,
however nothing about darkmatter and baryon fraction.

[Moderator's note: Since we have a pretty good idea of the total
density, the difference between that and the baryonic density is the
dark-matter density, more or less by definition. -P.H.]

[snip]

At the risk of opening up a new can of worms what do people think of the
new paper from Jamie Farnes at Oxford which seeks to unite dark energy
and dark matter as a negative mass fluid filling all of empty space (if
I have understood his paper correctly). It seems to work... title:

A Unifying Theory of Dark Energy and Dark Matter: Negative Masses and
Matter Creation within a Modified =CE=9B CDM Framework

https://arxiv.org/abs/1712.07962

Arxiv link but now also in A&A'. It makes some testable predictions.

--
Regards,
Martin Brown
 




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