Dark matter swirling into a black hole?

"bbbl67" wrote in message
ups.com...
On Jan 2, 10:16 pm, Craig Markwardt
wrote:
Getting a black hole to "suck up" even normal matter is actually
rather difficult. Of course there will be a very small fraction of
gas and stars that free-fall directly into the black hole. However,
most will not. Most normal matter in our galaxy is not gravitational
bound to the black hole in the center. The tiny fraction that is
bound probably got that way via tidal interactions and frictional
dissipation, which then forms an accretion disk. Even then, it is
fairly difficult to push matter into the black hole, since a large
amount of potential energy and angular momentum must be removed.
However, accretion disks are highly viscuous and turbulent, and a
small amount of mass transport does occur.

Looking at the mechanisms quoted above for binding matter to a black
hole and pushing it in: "tidal interactions" - "frictional
dissipation" - "accretion disk" - "viscuous" - "turbulent".
None of these effects is known to apply to dark matter since then
all require normal matter (electromagnetic) interactions.

So, Dark Matter doesn't interact with itself anymore than it interacts
with Normal Matter?

I believe that is the current understanding and it seems to
be borne out by the recent evidence from the Bullet Cluster:

http://antwrp.gsfc.nasa.gov/apod/ap060824.html

The gas in the two parts of the cluster interacted to create
the "bullet" shaped shock front but the blue clouds of dark
matter passed through each other unaffected.

George

On Jan 5, 9:05 am, "George Dishman" wrote:
I believe that is the current understanding and it seems to
be borne out by the recent evidence from the Bullet Cluster:

http://antwrp.gsfc.nasa.gov/apod/ap060824.html

The gas in the two parts of the cluster interacted to create
the "bullet" shaped shock front but the blue clouds of dark
matter passed through each other unaffected.

I've seen that picture before too. How do we know that those two blue
"dark matter clouds" are dark matter that came from opposite sides of
the cluster and passed through each other (as they said in the
caption)? How do we know that it isn't just dark matter slowly
following the lead of the two red clouds of x-ray gas? Those two blue
clouds seem to be set pretty dead-center upon the galaxies within those
two colliding clusters. So, it looks like the x-ray clouds have
collided far faster than the galaxies *AND* the dark matter of that
cluster.

Now they said that the galaxies of that cluster contain far less mass
than the free intergalactic x-ray gas in that cluster, however galaxies
contain far more concentrated matter than the x-ray clouds. Isn't it
possible that concentrations of matter alter the equations of gravity,
kind of like an exponential decay based on concentration? In the 300
years since Newton's laws about gravity, we've seen one major
modification to it, called the Theories of Relativity. The Newton's
Laws are now a subset of GTR. Quantum mechanics seems to suggest that
GTR isn't complete at the microscopic level, so who's to say it's
complete at other levels either? Since we've never been to
intergalactic space (never even been in interstellar space, for that
matter), what if another level of gravitational laws are discovered
which we could not detect within the confines of our solar system?

Secondly, neutrinos were considered a dark matter in the early part of
the 20th century, because they did not interact with normal matter
almost at all either. But their theoretical existence originally came
out of equations in nuclear reactions. Which allowed some people to
devise ways of trying to detect neutrinos eventually. What sort of
equations do today's Dark Matter arise from, other than as a desire to
keep the bookkeeping on today's equations for gravity straight?

bbbl67 wrote:

On Jan 5, 9:05 am, "George Dishman" wrote:
I believe that is the current understanding and it seems to
be borne out by the recent evidence from the Bullet Cluster:

http://antwrp.gsfc.nasa.gov/apod/ap060824.html

The gas in the two parts of the cluster interacted to create
the "bullet" shaped shock front but the blue clouds of dark
matter passed through each other unaffected.

I've seen that picture before too. How do we know that those two blue
"dark matter clouds" are dark matter that came from opposite sides of
the cluster and passed through each other (as they said in the
caption)? How do we know that it isn't just dark matter slowly
following the lead of the two red clouds of x-ray gas?

We know dark matter interacts gravitationally because
that is how we know it exists in the first place. It couldn't
"following the lead" because there is nothing to stop the
two falling together. Think how it would look if you were
moving along with them.

Those two blue
clouds seem to be set pretty dead-center upon the galaxies within those
two colliding clusters.

Yes, if the blue cloud on the left was trailing behind the
red cloud and galaxies on the right (and vice versa) it
would be a remarkable coincidence that the large cloud
associated with the small group of galaxies happened
to match the location of the large group of galaxies that
is pulling along the small blue cloud :-o

So, it looks like the x-ray clouds have
collided far faster than the galaxies *AND* the dark matter of that
cluster.

No, it looks to me like the small cluster of galaxies on the
right is associated with the small cloud of dark matter and
that they have not been separated while the small red cloud
has been pushed slightly to the left by the passage of the
large cloud and cluster that now lies to the left.

Now they said that the galaxies of that cluster contain far less mass
than the free intergalactic x-ray gas in that cluster, however galaxies
contain far more concentrated matter than the x-ray clouds. Isn't it
possible that concentrations of matter alter the equations of gravity,
kind of like an exponential decay based on concentration?

That sort of idea is where MOND comes from, and some
people are continuing to work on it, but it has problems
fitting other data. In fact I think there are difficulties in
getting it to predict gravitational lensing where we see
specific arcs but I don't know any details.

In the 300
years since Newton's laws about gravity, we've seen one major
modification to it, called the Theories of Relativity. The Newton's
Laws are now a subset of GTR. Quantum mechanics seems to suggest that
GTR isn't complete at the microscopic level, so who's to say it's
complete at other levels either? Since we've never been to
intergalactic space (never even been in interstellar space, for that
matter), what if another level of gravitational laws are discovered
which we could not detect within the confines of our solar system?

Certainly, dark energy looks like such a modification that
may be needed at very large scales, but that sort of
modification isn't going to work on galactic scales which
are much smaller than the cosmological range.

Secondly, neutrinos were considered a dark matter in the early part of
the 20th century, because they did not interact with normal matter
almost at all either. But their theoretical existence originally came
out of equations in nuclear reactions. Which allowed some people to
devise ways of trying to detect neutrinos eventually. What sort of
equations do today's Dark Matter arise from, other than as a desire to
keep the bookkeeping on today's equations for gravity straight?

That only works where there is some matter such that the
equations are non-zero. The search for dark matter galaxies
where there is very little visible matter should allow us to
rule that out. Hence the current interest in such searches.

George

In article , Yousuf Khan
wrote:

If Dark Matter exists, and the only way normal matter interacts with it
is through gravity, then shouldn't there be Dark Matter vortex swirling
into one of the biggest sources of normal matter mass around, i.e. a
black hole?

A black hole is not a source of normal matter

In fact, shouldn't the black hole be getting bigger by
several fold, just by fattening up with Dark Matter, which is supposed
to be an order of magnitude more prevalent than Normal Matter?

From a far enough distance, a black hole is the same as any other large
mass. It is not some cosmic hoover.

A black
hole would then be growing more massive even if no sources of normal
matter are nearby to feed it.

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