Hubble makes 3D dark matter map

In article ,
" writes:

B. Why, in the name of all we scientists are supposed to hold dear, do
intelligent scientists who are fully aware of these microlensing
results act like the observational results do not exist?

Who has done so? These are observations about dark matter WITHIN a
galaxy. If the same concentration of these objects existed in
intergalactic space, then the microlensing signal would be incompatible
with observations. References have been provided so many times you've
made this dubious claim that I will no longer do so and let the readers
draw their conclusions about who is deluded.

In article ,
wrote:

The point is that if dark matter is clumped up, wast regions might
be*sufficiently empty that it might be difficult to observe. You can only
see clumped up dark matter by observing the light that passes through it.

OK so far.* Now let's talk about what this clumped-up matter is made
of.* I thought that we were considering the possibility that it was
stuff with a lot of hydrogen gas in it.* We know a lot about what
stuff with a lot of hydrogen gas in it looks like when it's clumped up
on various size scales: if it's sufficiently densely clumped, we call
it "stars" or "brown dwarfs"; if it's somewhat less clumpy, we call it
"protostars," "molecular clouds," "gaseous nebulae," or a variety of
other things depending on context.* All of those things are observable
in a variety of different ways.* As a result, we have good estimates
of how much of them there are in our Galaxy, and it's not enough to be
the Galactic dark matter.

So if there is any hydrogen in the dark matter, it should be thin.

Regardless whether it is clumped up or not, it is hard to observe.

Hard, maybe --* I'll let the people who do it give opinions on that --
but not impossible.* On the contrary, observations of clumps of gas
is done all the time.* Honest, a huge amount is known about how
the gas in our Galaxy is distributed.

If it
is clumped up, the*regions must be*sufficiently narrow to be hard to
observe with todays telescopes. It means that it cannot consist of wast,
dense clouds. Assume, just as a thought experiment, that it consists
mainly of small black holes. Would it then be observable?

There probably is some parameter space for black holes as candidates
for the Galactic dark matter.* There are constraints on how big they
can be to have avoided detection by microlensing surveys, but I'd
guess that if you choose the right sizes you might be able to "hide"
them.* (There would then be all sorts of interesting puzzles about how
they formed in the first place.)

There is another post that suggest that (if I got it right) there can
indeed be a lot of small black holes, whatever their size may be, or at
least other clumped up stuff. The Chandrasekhar limit is around 1.4 solar
masse for a collapse to a neutron star, and a black hole must be bigger, r
so I would think. Unless it is possible for particles to tunnel out of
black holes, and these are old black holes, on their way to evaporate.

Another curious fact is*that for example Andromeda and Milky Way are
barred galaxies. So the density of dark matter is different towards the
hub, as the logarithmic*spirals are*due to dark matter. I got it that the
dark matter proportion*towards the hub should be bigger. It then lies in
line with my idea that dark matter can be produced via tunneling from
the*black*hole at the center of the galaxy.

It would be*interesting to know if there is something wrong with my reasoning.

--
Hans Aberg

Thus spake "
On Jan 30, 11:12 am, wrote:

-- that the best way to make a viable model in which the Galactic dark
matter consisted of black holes would be to make them much, much
smaller than a solar mass. That would, if I'm not mistaken, make the
microlensing signal hard to detect.


1. Several microlensing groups have independently observed
microlensing events with estimated masses for the lensing objects in
the 0.1 to 0.6 solar mass range.



Reasonable questions:

A. If these are not black holes, what are they?


the obvious answer is that they are red dwarfs.

B. Why, in the name of all we scientists are supposed to hold dear, do
intelligent scientists who are fully aware of these microlensing
results act like the observational results do not exist?

I don't think they act like the observational results do not exist. I
think they act like they are not very interesting. We don't know how
many red dwarfs there are. We do know that they are very numerous, that
we are finding them all the time, that they are not easy to find
especially at distance. There just doesn't seem anything of earth
shattering importance here.

C. When there is scientific evidence for actual stellar-mass dark
matter objects, why do scientists focus all their attention on
completely hypothetical "Cold Dark Matter" which has been a dependable
"no show" in 100s of experiments run over the last few decades?

Because, however many of them there are, these stellar mass dark matter
objects do not, and cannot, have the properties required of the cold
dark matter, which seems to be required by other observations.


Regards

--
Charles Francis
substitute charles for NotI to email

In article ,
wrote:

[...]

3. The estimated abundances for these objects ranges from roughly 10
to 30 percent of the estimated abundance of galactic dark matter. That
means that there is observational evidence for a very large number of
these mystery objects.

[...]

B. Why, in the name of all we scientists are supposed to hold dear, do
intelligent scientists who are fully aware of these microlensing
results act like the observational results do not exist?

I'm not sure whom you're accusing of this. As far as I know, everyone
working in the field is aware that these objects exist and is
also aware that a majority of the dark matter must be something else
besides these objects (see your 10%-30% comment above).

C. When there is scientific evidence for actual stellar-mass dark
matter objects, why do scientists focus all their attention on
completely hypothetical "Cold Dark Matter" which has been a dependable
"no show" in 100s of experiments run over the last few decades?

For one thing, because 30% 100%. For another thing, because there
are at least three independent lines of evidence showing that the
density of baryons (atomic matter) in the Universe is much lower than
the density of all matter, and therefore that nonbaryonic dark matter
must exist. Those arguments could all be wrong (although personally I
think it's unlikely), but at the very least they suggest that
nonbaryonic dark matter is worth searching for.

(In case anyone's wondering, the three lines of evidence I was referring
to are big-bang nucleosynthesis, the angular power spectrum of the
microwave background radiation, and the fact that large-scale structure
formation doesn't work with only baryonic matter.)

-Ted

--
[E-mail me at , as opposed to .]

In article ,
Hans Aberg wrote:
In article ,
wrote:

OK so far.* Now let's talk about what this clumped-up matter is made
of.* I thought that we were considering the possibility that it was
stuff with a lot of hydrogen gas in it.* We know a lot about what
stuff with a lot of hydrogen gas in it looks like when it's clumped up
on various size scales: if it's sufficiently densely clumped, we call
it "stars" or "brown dwarfs"; if it's somewhat less clumpy, we call it
"protostars," "molecular clouds," "gaseous nebulae," or a variety of
other things depending on context.* All of those things are observable
in a variety of different ways.* As a result, we have good estimates
of how much of them there are in our Galaxy, and it's not enough to be
the Galactic dark matter.

So if there is any hydrogen in the dark matter, it should be thin.

In that case, it'd be seen as absorption features in the light from
background stars. I promise you, it's really really hard (i.e.,
impossible) to hide enough hydrogen-rich matter in the Galaxy to be a
significant contributor to the dark matter.

-Ted


--
[E-mail me at , as opposed to .]

In article ,
wrote:

So if there is any hydrogen in the dark matter, it should be thin.

In that case, it'd be seen as absorption features in the light from
background stars.

If there is enough to result in sufficiently strong*absorption lines.

I promise you, it's really really hard (i.e.,
impossible) to hide enough hydrogen-rich matter in the Galaxy to be a
significant contributor to the dark matter.

Whoever has done a very good job, whatever the dark matter might be.

If it consists of normal matter in some form, then it should be*observable
by some means. But perhaps current observation methods are not enough,
yet.

--
Hans Aberg

On Jan 31, 10:12 am, wrote:

For one thing, because 30% 100%. For another thing, because there
are at least three independent lines of evidence showing that the
density of baryons (atomic matter) in the Universe is much lower than
the density of all matter, and therefore that nonbaryonic dark matter
must exist. Those arguments could all be wrong (although personally I
think it's unlikely), but at the very least they suggest that
nonbaryonic dark matter is worth searching for.

(In case anyone's wondering, the three lines of evidence I was referring
to are big-bang nucleosynthesis, the angular power spectrum of the
microwave background radiation, and the fact that large-scale structure
formation doesn't work with only baryonic matter.)



Primordial black holes count as nonbaryonic dark matter. Therefore it
is possible, and note I say possible, that all of the dark matter
could in principle be composed of primordial black holes. In this case
there would be no need for any particle-mass (CDM) dark matter.

This remains to be determined empirically, which is the only way to
reliably decide things in science.

If the dark matter turns out to be stellar scale primordial black
holes, and we should know one way or the other within 5-10 years
(maybe as soon as GLAST takes a good look), then please, in the name
of science, do not say they are hypermassive CDM particles, and fit
remarkably well with the standard model. Deal?

Rob

On Jan 31, 4:08 am, Oh No wrote:

the obvious answer is that they are red dwarfs.


Those astrophysicists who have studied the dark matter issue in great
detail and depth have esitmated that red dwarfs could, at most,
contribute 5% of the dark matter. Published numbers are often in the
1% to 3% range. So at face value, the red dwarf explanation is
dubious. Although they are present in large numbers, and relatively
dim, if they were the dark matter (and 5-10 times more common) they
would be optically detectable.

Could there be something unexpectedly wrong with the assumptions
involved in estimates used to rule out red dwarfs as the primary
component of the dark matter? Of course, this is science not received
wisdom. But as in the case with CDM, one who takes this approach is de-
emphasizing published, positive observational detections and putting
one's money on hypothetical entities or hypothetical errors.

Why don't we just say: there is observational evidence for the
possibility of a large population of stellar-mass black holes, but we
await definitive confirmation?

Robert L. Oldershaw

On Jan 31, 3:41 am, (Phillip Helbig---
remove CLOTHES to reply) wrote:
In article ,

" writes:
B. Why, in the name of all we scientists are supposed to hold dear, do
intelligent scientists who are fully aware of these microlensing
results act like the observational results do not exist?

Who has done so? These are observations about dark matter WITHIN a
galaxy. If the same concentration of these objects existed in
intergalactic space, then the microlensing signal would be incompatible
with observations. References have been provided so many times you've
made this dubious claim that I will no longer do so and let the readers
draw their conclusions about who is deluded.


At best, in only one-out-of-10 discussions of the nature of the dark
matter are the microlensing results even mentioned, and then usually
in a cursory fashion. Then the authors usually wax prosaic about the
merits of the CDM hypothesis. You ask: "Who?" Answer: Nearly all
astrophysicists.

Who introduced this bizarre concept that the dark matter is evenly
spread throughout spacetime? I have never done so, and you can verify
that by taking the time to read the "Critical Test..." thread. It is
you that introduced this bizarre concept, probably so you could shoot
it down in good old straw-man fashion. It has always been clear to me
that dark matter and conventional matter have similar distributions.
Therefore your criticism lacks merit.

Capitalizing whole words and phrases is the online equivalent of
shouting. I suggest that members of this newsgroup should refrain from
this activity, since it is not in keeping with the spirit of science,
and has more in common with the demagogery of politics.

Robert L. Oldershaw

In article ,
wrote:

Primordial black holes count as nonbaryonic dark matter. Therefore it
is possible, and note I say possible, that all of the dark matter
could in principle be composed of primordial black holes. In this case
there would be no need for any particle-mass (CDM) dark matter.

This remains to be determined empirically, which is the only way to
reliably decide things in science.

If the dark matter turns out to be stellar scale primordial black
holes, and we should know one way or the other within 5-10 years
(maybe as soon as GLAST takes a good look), then please, in the name
of science, do not say they are hypermassive CDM particles, and fit
remarkably well with the standard model. Deal?

Well, whether they're "hypermassive CDM particles" or not would be a
purely semantic question, and I can't make myself care too much about
it. They would certainly be CDM, more or less by definition of that
term. Since the word "particle" in physics usually means something
other than black holes, I'll happily agree that they probably
shouldn't be called particles.

Personally, I think it'd be great fun if the dark matter turned out to
be primordial black holes. I'm certainly not wedded to the particle-physics
WIMP paradigm for the dark matter: I have been generally persuaded over
the years that it's the simplest and best-motivated model consistent
with the data, but that falls far, far short of being convincing evidence
that it's actually true.

I don't know the state of play regarding observational constraints on
primordial black holes as the dark matter: there are a bunch of
different constrainst, which depend on the typical size scale of the
black holes, and I have no idea which portions of that parameter space
are ruled out and which are still viable. If anyone is up on that
subject, it'd be fun to hear about it.

-Ted

--
[E-mail me at , as opposed to .]