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

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.

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

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.