Hubble makes 3D dark matter map

In article ,
" writes:

Primordial black holes count as nonbaryonic dark matter.

Right. Hawkins suggested this about 12 years ago in a paper in which he
suggested that much long-term QSO variability was caused by
microlensing. We understand microlensing. We can make predictions. We
can compare them to observations.

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.

It is possible in the sense that the universe COULD have been that way.
However, it is not. If the dark matter is in black holes (of the masses
you claim), then it would cause microlensing in a manner not compatible
with observations.

Your theory is good in that it makes testable predictions. However,
those predictions have been tested and found wanting. Move on.

In article ,
writes:

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.

http://www.arxiv.org/abs/astro-ph/0306434

Although controversial, the scenario of microlensing as the
dominant mechanism for the long-term optical variability of quasars
does provide a natural explanation for both the statistical
symmetry, achromaticity and lack of cosmological time dilation in
quasar light curves. Here, we investigate to what extent dark
matter populations of compact objects allowed in the currently
favored Omega_M=0.3, Omega_Lambda=0.7 cosmology really can explain
the quantitative statistical features of the observed variability.
We find that microlensing reasonably well reproduces the average
structure function of quasars, but fails to explain both the high
fraction of objects with amplitudes higher than 0.35 magnitudes and
the mean amplitudes observed at redshifts below one. Even though
microlensing may still contribute to the long-term optical
variability at some level, another significant mechanism must also
be involved. This severely complicates the task of using
light-curve statistics from quasars which are not multiply imaged
to isolate properties of any cosmologically significant population
of compact objects which may in fact be present.

In other words, if the objects are there, they would have a certain
microlensing signature. This is not observed. MAYBE they are there and
another source of variability is so constructed so that it hides these
objects and the combination matches the observations---but this sounds
like angels pushing the planets along their orbits.

"HA" == Hans Aberg writes:

HA In article ,
HA 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.

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

This is an illustration of what Ted meant when he suggested you know
what non-dark matter can do. Absorption of quasar light is seen by
clouds of intergalactic hydrogen. Measurable absorption is seen for
clouds with column densities of order 1E14 hydrogen atoms/cm^2.
Suppose that these clouds are 1 kpc in size. (I don't know the size
estimates off the top of my head, but if anything I've probably
underestimated their sizes.) Thus, the density of these clouds is of
order

n ~ 0.03 hydrogen atoms/m^3

Less than 1 hydrogen atom per cubic meter of space. Moreover, if I've
underestimated the size of one of these clouds (which is quite
possible), then I've *overestimated* the density.

Yes, one could imagine hiding hydrogen by making it even less dense
than these clouds, but then one has to answer how much mass would
result. I suspect it is fairly easy to show that any thin gruel of
hydrogen that we've missed wouldn't have a substantial mass.

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On Feb 1, 5:57 pm, (Phillip Helbig---
remove

http://www.arxiv.org/abs/astro-ph/0306434
In other words, if the objects are there, they would have a certain
microlensing signature. This is not observed. MAYBE they are there and
another source of variability is so constructed so that it hides these
objects and the combination matches the observations---but this sounds
like angels pushing the planets along their orbits.


You reference a single paper from 2003 and then imply microlensing is
not a reasonable interpretation of the variability in QSO light
curves.

However, many papers have been published on this subject and some note
that variations in the continuum flux (rather than the BLR
fluctuations) are consistent with expectations based on microlensing
by stellar-mass objects. An example is astro-ph/0701325.

Another interesting paper is astro-ph/0701420, which shows data for a
very long-term monitoring of a blazar. Varaitions in the light curve
show 2 significant timescales: 1-3 months and 5-13 years. These time
scales are roughly consistent with planetary-mass and stellar mass
objects. Quite interesting, I think.

The bottom line is that the issue of whether QSO variations can, at
least partially, be explained in terms of stellar-mass dark matter
objects, has not been settled. At least not in the minds of
astrophysicists who view the situation objectively. I do not think
that it is fair or accurate to treat the matter as a closed one.

Robert L. Oldershaw

On Feb 1, 5:55 pm, (Phillip Helbig---
remove .

It is possible in the sense that the universe COULD have been that way.
However, it is not. If the dark matter is in black holes (of the masses
you claim), then it would cause microlensing in a manner not compatible
with observations.

Your theory is good in that it makes testable predictions. However,
those predictions have been tested and found wanting. Move on.


If the dark matter turns out to be something other than what I have
predicted (see thread entitled "Critical Test..." at this newsgroup),
then I will be happy to admit error and "move on". I assume that if
the prediction is correct, on the other hand, that you will do the
same. We will know who is right in 5 years, tops. We do not have a
scientific answer at present.

Robert L. Oldershaw

In article , Joseph Lazio
wrote:

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

This is an illustration of what Ted meant when he suggested you know
what non-dark matter can do. Absorption of quasar light is seen by
clouds of intergalactic hydrogen. Measurable absorption is seen for
clouds with column densities of order 1E14 hydrogen atoms/cm^2.
Suppose that these clouds are 1 kpc in size. (I don't know the size
estimates off the top of my head, but if anything I've probably
underestimated their sizes.) Thus, the density of these clouds is of
order

n ~ 0.03 hydrogen atoms/m^3

Less than 1 hydrogen atom per cubic meter of space. Moreover, if I've
underestimated the size of one of these clouds (which is quite
possible), then I've *overestimated* the density.

Yes, one could imagine hiding hydrogen by making it even less dense
than these clouds, but then one has to answer how much mass would
result. I suspect it is fairly easy to show that any thin gruel of
hydrogen that we've missed wouldn't have a substantial mass.

If there is any hydrogen dark matter, it might be rather quickly sucked up
in some clumping process, causing most of the space in between to be
rather empty. Between the galaxies, this clumping might be the formation
of new, small galaxies, which are hard to observe, due to size, and that
they rather quickly get absorbed into larger galaxies. Within a galaxy,
this might be the forming of stars.

There might be a balance between black holes, and these other objects. It
seems me that black holes can be continuously formed by collapse of dark
and lit matter. And if black hole tunneling is possible, it should produce
hydrogen, or infancy, matter, for the forming of other, in due time,
mainly lit, objects.

So, why would the black holes need to be (as mentioned in other posts of
this thread) "primordial", which I gather would imply they were formed*at
a Big Bang event?

--
Hans Aberg

In article ,
Hans Aberg wrote:

So, why would the black holes need to be (as mentioned in other posts of
this thread) "primordial", which I gather would imply they were formed*at
a Big Bang event?

One reason is that we have various constraints on the density of
atomic matter (often called the "baryon density"), which show that
it's significantly less than the density of all matter. Some of these
constraints measure the baryon density now, but others measure the
baryon density at earlier times, specifically, the time of
recombination (z=1100, t=400,000 years) and the time of nucleosynthesis
(z ~ 10^9, t ~ 1 second). If the dark matter is black holes, and
if they formed from baryonic matter at times later than those,
then those bounds would be violated.

Aside from this, if you want to construct a model like this, you have
to work out when the black holes formed, and how efficient they were
at sucking up all of that gas, and what light-emitting or absorbing
processes happened during that time. I suspect it's hard to construct
such a model that doesn't run afoul of observations. We've observed
the Universe a lot, at a lot of different redshifts, at a lot of
different wavelengths. Unless you can suck all of the matter up very
efficiently into black holes at very early times, I think you're going
to have a tough time. Even then, you have the baryon density problem
above and the quasar microlensing issue Phillip Helbig has mentioned.

If you want to try to solve all of these problems, go for it! Step 1,
as I've mentioned before, is to learn a lot about what we already
know about the distribution of visible stuff in the Universe.

-Ted

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

On Feb 2, 10:04 am, (Hans Aberg) wrote:

So, why would the black holes need to be (as mentioned in other posts of
this thread) "primordial", which I gather would imply they were formed at
a Big Bang event?


If these black holes formed as the end-product of normal stellar
evolution, i.e., as the collapsed objects left after very massive
stars go supernova, then the stars that produced them would have
injected too many heavy elements into the local universe. This excess
of heavy elements appears to have been ruled out empirically.

Therefore it appears that non-baryonic dark matter is virtually
mandatory. And so the black holes would have had to "form" in some
other manner. One possibility is that they are the generic product of
a Big Bang in an "early" universe, hence "primordial".

It is always possible that there is some glitch in the reasoning
above, but no one has identified one yet.

Robert L. Oldershaw

"HA" == Hans Aberg writes:

HA In article , Joseph
HA Lazio
HA wrote:

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

This is an illustration of what Ted meant when he suggested you
know what non-dark matter can do. Absorption of quasar light is
seen by clouds of intergalactic hydrogen. Measurable absorption is
seen for clouds with column densities of order 1E14 hydrogen
atoms/cm^2. Suppose that these clouds are 1 kpc in size. (...)
Thus, the density of these clouds is of order

n ~ 0.03 hydrogen atoms/m^3

Less than 1 hydrogen atom per cubic meter of space. Moreover, if
I've underestimated the size of one of these clouds (...), then
I've *overestimated* the density.

Yes, one could imagine hiding hydrogen by making it even less dense
than these clouds, but then one has to answer how much mass would
result. I suspect it is fairly easy to show that any thin gruel of
hydrogen that we've missed wouldn't have a substantial mass.

Re-reading my answer, I should add the caveat that thinly ionized
hydrogen would of course not show any absorption lines. However, if
there are any other elements mixed together (e.g., oxygen) with the
hydrogen, then one might be able to detect absorption from them.
Notably, the FUSE, Chandra, and XMM-Newton have all detected
absorption from highly ionized oxygen and neon. Indeed, it is now
thought that many of the baryons in the Universe are in the form of a
warm-hot intergalactic medium (WHIM) that is at a temperature of
around 10^6 K.

HA If there is any hydrogen dark matter, it might be rather quickly
HA sucked up in some clumping process, causing most of the space in
HA between to be rather empty.
[...]

This sounds like Mark Walker's idea of dense, AU-sized molecular
clouds. Yes, one can "hide" a substantial amount of hydrogen this
way. However, to do so requires a certain amount of fine-tuning,
getting all of the conditions just so in order to avoid detecting the
material.


[...]
HA So, why would the black holes need to be (...) "primordial", which
HA I gather would imply they were formed*at a Big Bang event?

I think somebody (Ted, Phillip?) has already discussed this. Briefly,
we have estimates for the density of baryonic matter and the total
density of matter in the Universe. The density of matter is larger
than the density of baryonic matter. As black holes are formed from
baryonic matter---whether it be from the collapse of stars or clouds
of hydrogen gas, both are baryonic matter---black holes cannot account
for all matter in the Universe. There needs to be some non-baryonic
dark matter.

Indeed, we already know of one kind of non-baryonic dark matter,
neutrinos. They are not baryons, they have mass, and they do not
interact via the electromagnetic force (i.e., with light). If we know
of one kind of non-baryonic dark matter, it is not too difficult to
think that there might be other kinds.

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

In article ,
" wrote:

So, why would the black holes need to be (as mentioned in other posts of
this thread) "primordial", which I gather would imply they were formed at
a Big Bang event?

If these black holes formed as the end-product of normal stellar
evolution, i.e., as the collapsed objects left after very massive
stars go supernova, then the stars that produced them would have
injected too many heavy elements into the local universe. This excess
of heavy elements appears to have been ruled out empirically.

Therefore it appears that non-baryonic dark matter is virtually
mandatory. And so the black holes would have had to "form" in some
other manner. One possibility is that they are the generic product of
a Big Bang in an "early" universe, hence "primordial".

It is always possible that there is some glitch in the reasoning
above, but no one has identified one yet.

The black holes would have to suck up heavy elements as well. When a star
collapses, the black hole need not suck*up heavy*elements immediately, but
it might do that later, when the local area has calmed down. The idea is
that the heavy elements falling into the black hole are broken up inside
it, and if matter can tunnel out, it will, via some nucleosynthesis at the
black hole surface, be the infancy matter that small, nearby galaxies are
formed of.

--
Hans Aberg