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#1
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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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