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More on LIGO, DM, PBHs, CIB and CXB



 
 
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  #1  
Old July 21st 16, 12:55 PM posted to sci.astro.research
Robert L. Oldershaw
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Default More on LIGO, DM, PBHs, CIB and CXB

[Moderator's note: Unnecessary attribution removed. -P.H.]

There is a very interesting new paper on the topics of PBHs and the DM.

http://arxiv.org/abs/1607.06077

Title: Primordial Black Holes As Dark Matter
AUs: B. Carr et al

Take home lesson: It is difficult to put all the dark matter in PBHs if
their mass function is monochromatic but this is still possible if the
mass function is extended, as expected in many scenarios.

RLO
http://www3.amherst.edu/~rloldershaw

  #2  
Old July 23rd 16, 09:19 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Default More on LIGO, DM, PBHs, CIB and CXB

In article ,
"Robert L. Oldershaw" writes:=20

There is a very interesting new paper on the topics of PBHs and the DM.

http://arxiv.org/abs/1607.06077

Title: Primordial Black Holes As Dark Matter
AUs: B. Carr et al

Take home lesson: It is difficult to put all the dark matter in PBHs if
their mass function is monochromatic but this is still possible if the
mass function is extended, as expected in many scenarios.


Somewhat related to this, at a gravitational-lens conference in Leiden
last week there was a talk on planets as discovered by microlensing.
Take-home message was that for every star there is probably one
free-floating Jupiter-sized planet. That means a couple of hundred
billion in our galaxy, but comparing the mass of Jupiter to the mass of
the Sun, even this huge population is a negligible fraction of the dark
matter in the galaxy.
  #3  
Old July 23rd 16, 10:01 PM posted to sci.astro.research
Robert L. Oldershaw
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Posts: 617
Default More on LIGO, DM, PBHs, CIB and CXB

On Saturday, July 23, 2016 at 4:19:41 PM UTC-4, Phillip Helbig
(undress to reply) wrote:


Somewhat related to this, at a gravitational-lens conference in Leiden
last week there was a talk on planets as discovered by microlensing.
Take-home message was that for every star there is probably one
free-floating Jupiter-sized planet. That means a couple of hundred
billion in our galaxy, but comparing the mass of Jupiter to the mass of
the Sun, even this huge population is a negligible fraction of the dark
matter in the galaxy.


That is the current *estimate*, but "a couple of hundred billion
in our Galaxy" alone not a small number and certainly not zero (as
is the case for "WIMPs", "axions, "sterile neutrinos", etc).

Moreover, it should make any scientist wonder what other populations
of astrophysical objects have gone undetected. Maybe we have only
so far seen the tip of the proverbial iceberg when it comes to
previously unimagined and undetected astrophysical DM candidates.

RLO
http://www3.amherst.edu/~rloldershaw
  #4  
Old July 24th 16, 06:46 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Posts: 273
Default More on LIGO, DM, PBHs, CIB and CXB

In article ,
"Robert L. Oldershaw" writes:

Somewhat related to this, at a gravitational-lens conference in Leiden
last week there was a talk on planets as discovered by microlensing.
Take-home message was that for every star there is probably one
free-floating Jupiter-sized planet. That means a couple of hundred
billion in our galaxy, but comparing the mass of Jupiter to the mass of
the Sun, even this huge population is a negligible fraction of the dark
matter in the galaxy.


That is the current *estimate*,


EVERY observation is an estimate. There is no reason to think that this
is unduly provisional, that it will be revised upward, etc.

but "a couple of hundred billion
in our Galaxy" alone not a small number and certainly not zero (as
is the case for "WIMPs", "axions, "sterile neutrinos", etc).


Remember gravitational waves. How many decades between prediction and
observation? Absence of evidence is not evidence of absence.

The fact is that we don't know what dark matter is. As such, it makes
sense to search for ALL candidates.

As the paper which started this thread mentions, dark matter could be in
primordial black holes. However, not one single primordial black hole
has been observed.

One should have the same standards for all candidates.

It IS a small number in the sense that the total contribution to dark
matter is very small, almost negligible. There are many orders of
magnitude more neutrinos, an absolutely huge number, but their
contribution to the dark matter is also negligible.
  #5  
Old July 24th 16, 08:00 PM posted to sci.astro.research
Jos Bergervoet
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Posts: 126
Default More on LIGO, DM, PBHs, CIB and CXB

[Moderator's note: Original Message-ID header removed because it contained
an 8-bit character.]

On 7/24/2016 7:46 PM, Phillip Helbig (undress to reply) wrote:
In article ,
"Robert L. Oldershaw" writes:


..
As the paper which started this thread mentions, dark matter could be in
primordial black holes. However, not one single primordial black hole
has been observed.


Actually, the text in the paper goes like this:
".. if indeed the LIGO discovery is indicative of
PBHs making up the DM, .." (p2, last paragraph).
http://arxiv.org/abs/1605.04023
And for *those* black holes we can say that 4 of
them have been observed.

Or is it ruled out that they are PBHs? (That would
in fact be contrary to what the paper mentions..)

--
Jos

  #6  
Old July 24th 16, 11:58 PM posted to sci.astro.research
Robert L. Oldershaw
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Posts: 617
Default More on LIGO, DM, PBHs, CIB and CXB

On Sunday, July 24, 2016 at 3:00:59 PM UTC-4, Jos Bergervoet wrote:

Actually, the text in the paper goes like this:
".. if indeed the LIGO discovery is indicative of
PBHs making up the DM, .." (p2, last paragraph).
http://arxiv.org/abs/1605.04023
And for *those* black holes we can say that 4 of
them have been observed.


Also we have a very large number (at least 100 billion) MACHOs that
have been detected via microlensing. Andrew Gould published a paper
(ApJ, I think) that explored possible candidates and came to the
conclusion that primordial black holes were the best candidate.

We should await further observational evidence before deciding
whether or not PBHs are the dark matter.

Fixed ideas based on assumptions are really not a good idea in science.

RLO
http://www3.amherst.edu/~rloldershaw

[[Mod. note -- If you could post a reference to the exact paper you're
referring to, that would be helpful. Andrew Gould has written a lot of
papers, but a quick google scholar search just now for author "Gould",
journal "Astrophysical Journal", containing exact phrase "primordial
black hole", turned up three references none of which look the one
you're referring to.
-- jt]]
  #7  
Old July 26th 16, 11:30 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Posts: 273
Default More on LIGO, DM, PBHs, CIB and CXB

In article ,
"Robert L. Oldershaw" writes:

Also we have a very large number (at least 100 billion) MACHOs that
have been detected via microlensing.


To quote you, that is an ESTIMATE. Nowhere near this many microlensing
events have been observed. This is an extrapolation. I'm not saying
it's wrong, just pointing out that it is wrong to refer to what you like
as "observations" and what you don't like as "estimates".

Andrew Gould published a paper
(ApJ, I think) that explored possible candidates and came to the
conclusion that primordial black holes were the best candidate.


Let's assume he did.

We should await further observational evidence before deciding
whether or not PBHs are the dark matter.


For the umpteenth time, it has been definitively ruled out that PBHs can
make up a significant fraction of the dark matter except perhaps (as the
Carr et al. paper points out) in some mass ranges which are not probed
by microlensing. So, discussing PBHs, dark matter, and microlensing is
discussing something which is not relevant.

Fixed ideas based on assumptions are really not a good idea in science.


Indeed. :-)
  #8  
Old July 27th 16, 09:53 PM posted to sci.astro.research
Richard D. Saam
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Posts: 240
Default More on LIGO, DM, PBHs, CIB and CXB

On 7/26/16 5:30 PM, Phillip Helbig (undress to reply) wrote:
In article ,
"Robert L. Oldershaw" writes:

Also we have a very large number (at least 100 billion) MACHOs that
have been detected via microlensing.


For reference, I would like to see a calculation
of maximum object number and size
given apparent inter extra galactic space optical transparency.
The Beer-Lambert law may be applicable.

Richard Saam

  #9  
Old July 27th 16, 09:53 PM posted to sci.astro.research
Robert L. Oldershaw
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Posts: 617
Default More on LIGO, DM, PBHs, CIB and CXB

On Tuesday, July 26, 2016 at 6:30:13 PM UTC-4, Phillip Helbig (undress to reply) wrote:


For the umpteenth time, it has been definitively ruled out that PBHs can
make up a significant fraction of the dark matter except perhaps (as the
Carr et al. paper points out) in some mass ranges which are not probed
by microlensing. So, discussing PBHs, dark matter, and microlensing is
discussing something which is not relevant.


The recent LIGO events suggest that a significant fraction of the dark
matter could be in 10-30 solar-mass black holes. MACHO results are
consistent with up to 20% of the dark matter in the form of black holes
in the 0.5 solar mass range.

You seem to be unjustifiably dismissive of stellar-mass PBHs. This is
especially inappropriate when there is so much uncertainty in our
current knowledge about the dark matter.

Let's not rush to absolute judgments.

RLO
http://amherst.edu/~rloldershaw

  #10  
Old July 27th 16, 11:54 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Posts: 273
Default More on LIGO, DM, PBHs, CIB and CXB

In article ,
"Robert L. Oldershaw" writes:

The recent LIGO events suggest that a significant fraction of the dark
matter could be in 10-30 solar-mass black holes.


I think that you would probably accuse anyone else extrapolating from
two events of being over-confident.

The 10--30 solar-mass range is not probed by microlensing so, yes, some
could be there.

MACHO results are
consistent with up to 20% of the dark matter in the form of black holes
in the 0.5 solar mass range.


Let's grant this. Still, most of the dark matter cannot be in objects
of mass which would show up in microlensing. So microlensing has not
detected "the" dark matter.

You seem to be unjustifiably dismissive of stellar-mass PBHs.


Because the observational constraints---as explained in detail in the
Carr et al. paper---are quite tight.

This is
especially inappropriate when there is so much uncertainty in our
current knowledge about the dark matter.

Let's not rush to absolute judgments.


I'm not. It is you who "knows" what the dark matter is and who rushes
to judgements about the significance of negative results. Again,
absence of evidence is not evidence of absence. One is, correctly, not
required to prove one's innocence in court.

While I see no reason why most or all dark matter can't be in PBHs as
long as the corresponding mass range does not conflict with
observations, it does look contrived if there is just enough room in
just those mass ranges which are not (yet) accessible observationally.
Sort of like of "God of the gaps" theology---technically possible, but
contrived.

With WIMPs as well, there are ranges of parameter space which are not
probed by experiments. Why is this a mark against WIMPs, and a mark for
PBHs?
 




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